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GEOLOGY 


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14685-S 


DEPARTMENT  OF  THE  INTERIOR 

UNITED  STATES  GEOLOGICAL  SURVEY 

GEORGE  OTIS  SMITH,  Director 


Bulletin  446 


GEOLOGY 

I 

OF  THE 

BERNERS  BAY  REGION 

ALASKA 

BY 

ADOLPH  KNOPF 


WASHINGTON 

GOVERNMENT  PRINTING  OFFICE 

1911 


I 


^Digitized  by  the  Internet  Archive 
in  2015  • 


j 


https://archive.org/details/geologyofberners4434knop 


CONTENTS. 


Page. 

Preface,  by  Alfred  H.  Brooks 5 

Introduction 7 

History 8 

Production 8 

Geography ^ 9 

Situation  of  the  region 9 

Physical  features 9 

Climate  and  vegetation 10 

Glaciation 12 

Outline  of  geology  and  ore  deposits 12 

General  geology 14 

Berners  formation 14 

General  character  and  distribution 14 

Petrography 16 

Age  and  correlation 17 

Dikes 18 

Basic  volcanic  rocks 19 

General  character  and  distribution 19 

Petrography 19 

Contact-altered  phases 20 

Age 21 

Intrusive  felsites 21 

Quartz  diorite  gneiss 22 

General  character 22 

Petrography 22 

Contact  phenomena  and  age 23 

Jualin  diorite 24 

General  character  and  occurrence 24 

Petrography 24 

Age 25 

Hornblendite 25 

The  ore  bodies 26 

Introductory  statement 26 

Fissure  veins 26 

Stockworks 27 

Stringer  lodes 28 

Mineralogy  of  the  ore  deposits 29 

Introductory  statement 29 

Gold 29 

Copper 29 

Galena 29 

Sphalerite 29 

Chalcopyrite 29 

Pyrite 30 


3 


4 


CONTENTS. 


The  ore  bodies — Continued. 

Mineralogy  of  the  ore  deposits — Continued.  Page. 

Quartz 30 

Calcite 30 

Dolomite 30 

Feldspar 30 

Sericite 30 

Hornblende 31 

Epidote 31 

Chlorite 31 

Value  of  the  ores 31 

Fissure  and  vein-forming  processes 31 

Origin  of  the  ore  deposits 35 

Practical  deductions 36 

Descriptions  of  individual  mines  and  prospects 38 

Ivanhoe  mine 38 

Horrible  mine 39 

Ophir  group 39 

Bear  mine 39 

Kensington  mine 40 

Eureka  mine 42 

Comet  mine 42 

Johnson  mine 43 

Indiana  property 44 

Jualin  mine 44 

Fremming  property 47 

Greek  Boy  property 47 

Recent  Survey  publications  on  Alaska 49 

Index 57 


ILLUSTRATIONS. 


Page. 

Plate  I.  Topographic  map  of  the  Berners  Bay  region In  pocket. 

II.  Geologic  map  of  the  Berners  Bay  region In  pocket. 

Figure  1.  Sketch  of  Berners  Bay  region 9 

2.  Diagram  showing  strike  of  veins 27 

3.  Diagram  showing  dip  of  veins 27 

4.  Diagrammatic  section  along  the  Kensington  tunnel 41 


PREFACE. 


By  Alfred  H.  Brooks. 


The  general  plan  for  the  Alaskan  work  provides  first  for  recon- 
naissance surveys  which  it  is  intended  eventually  to  extend  over  the 
entire  Territory.  These  reconnaissance  surveys  are  followed  by  the 
detailed  mapping  of  the  most  important  mining  district. 

The  first  investigation  of  the  mineral  resources  of  southeastern 
Alaska  by  the  Geological  Survey  was  made  by  Becker®  in  1895. 
More  systematic  surveys  of  Alaska  were  begun  in  1898,  but  for  several 
years  the  demands  of  the  unexplored  regions  of  the  interior  prevented 
any  attention  being  given  to  the  coastal  provinces.  In  1901  a hasty 
examination  of  the  Ketchikan  district^  was  undertaken,  and  in  1903 
and  1904  reconnaissance  surveys  of  the  Juneau  and  Porcupine  dis- 
tricts^ were  completed.  Reconnaissance  surveys  have  been  continued 
in  southeastern  Alaska  up  to  the  present  time.  With  the  publication 
of  the  report  on  the  Wrangell  and  Ketchikan  districts^  in  1908  all  the 
most  important  mining  regions  were  covered.  There  still  remain, 
however,  extensive  areas  in  southeastern  Alaska  of  which  the  geology 
is  but  little  known. 

Meanwhile  some  detailed  geologic  studies  have  been  made.  In  1902 
and  1903  the  detailed  geologic^  and  topographic-^  mapping  of  the 
most  productive  part  of  the  Juneau  district  was  completed.  Between 
1906  and  1908  detailed  topographic  surveys  of  the  Kasaan  Peninsula, 
Karta  Bay,  and  Hetta  Inlet  copper-bearing  areas  were  completed. 
Owing  to  circumstances  beyond  the  control  of  the  writer,  the  results 
of  these  surveys  have  not  been  published,  but  it  is  hoped  that  they 
may  be  issued  during  1911.  Plans  for  detailed  studies  of  the  Berners 
Bay  region  were  formulated  in  1906,  when  a topographic  survey  of 
the  district^  was  made.  Owing  to  the  litigation  in  which  several  of 

a Becker,  G.  F.,  Reconnaissance  of  the  gold  fields  of  southern  Alaska,  with  some  notes  on  the  general 
geology:  Eighteenth  Ann.  Rept.  U.  S.  Geol.  Survey,  pt.  3, 1897,  pp.  1-86. 

b Brooks,  A.  H.,  Preliminary  report  on  the  Ketchikan  mining  district,  with  an  introductory  sketch  of  the 
geology  of  southeastern  Alaska:  Prof.  Paper  U.  S.  Geol.  Survey  No.  1,  1902. 

c Spencer,  A.  C.,  The  Juneau  gold  belt;  Wright,  C.  W.,  A reconnaissance  of  Admiralty  Island:  Bull. 
U.  S.  Geol.  Survey  No.  287,1906.  Wright, C.  W., The  Porcupine  placer  district:  Bull.  U.  S.  Geol.  Survey 
No.  236, 1905. 

d Wright,  C.  W.  and  F.  E.,  The  Ketchikan  and  Wrangell  mining  districts,  Alaska:  Bull.  U.  S.  Geol.  Sur- 
vey No.  347, 1908. 

c Spencer,  A.  C.,  Bull.  U.  S.  Geol.  Survey  No.  287, 1906. 

/Juneau  special  map,  U.  S.  Geol.  Survey,  1904. 

g Berners  Bay  special  map,  No.  581B,  U.  S.  Geol.  Survey,  1908. 


5 


6 


PREFACE. 


the  largest  mining  properties  of  the  district  have  been  involved,  the 
geologic  work  was  postponed  until  last  year  (1909),  when  the  settle- 
ment of  one  of  the  important  lawsuits  gave  promise  that  the  district 
would  soon  become  an  important  gold  producer. 

The  heavy  growth  of  timber,  the  thick  underbrush,  and  the  mat  of 
moss  mantle  the  bed  rock  of  much  of  this  region  to  such  an  extent  as 
to  make  detailed  geologic  surveys  almost  hopeless.  It  is  for  this  reason 
that  but  few  cartographic  units  have  been  used  in  representing  the 
geology.  It  is  believed,  however,  that  the  subdivisions  made  are 
sufficiently  detailed  so  that  the  geologic  map  may  serve  the  purpose  of 
the  prospector  as  well  as  outline  the  important  features  of  the  geology. 

Mr.  Knopf’s  studies  show  that  the  ore  bodies  occur  in  intrusive 
rocks  which  are  partly  of  post-Jurassic  or  post-Lower  Cretaceous  age. 
This  is  confirmative  of  the  views  previously  held,  of  which  definite 
proof  was  lacking.  It  affords  additional  evidence  of  the  synchroneity 
of  the  mineralization  of  south-central  Alaska  with  that  of  the  Mother 
Lode  district  of  California.  This  work  also  proves  that  the  sediments 
and  associated  greenstones  of  the  Juneau  gold  belt  previously  assigned 
to  the  Carboniferous  are  in  part  at  least  Mesozoic. 

This  report  is  based  on  studies  made  in  such  detail  as  the  physical 
conditions  permitted.  The  fact  that  none  of  the  mines  were  in  opera- 
tion hampered  to  a large  degree  the  investigations  of  the  ore  bodies. 
If  mining  develops  in  this  field  to  the  extent  which  seems  warranted 
by  the  knowledge  of  its  auriferous  deposits,  the  time  will  come  when 
a more  exhaustive  study  of  the  ore  bodies  should  be  undertaken. 


THE  BERNERS  BAY  REGION,  ALASKA. 


By  Adolph  Knopf. 


INTRODUCTION. 

The  Berners  Bay  region  forms  the  northwestern  extremity  of  the 
long  zone  of  auriferous  mineralization  on  the  mainland  of  southeastern 
Alaska  known  as  the  Juneau  gold  belt.  This  belt  has  a total  length 
of  100  miles  and  extends  southeastward  to  Windham  Bay,  60  miles 
southeast  of  Juneau.  A large  number  of  prospects  are  scattered 
along  the  gold  belt,  but  at  two  localities,  Juneau  and  Berners  Bay, 
there  is  a marked  clustering  of  producing  mines  or  of  potentially 
productive  ore  bodies. 

The  famous  Treadwell  group  of  mines,  the  Perseverance  mine,  and 
other  properties  of  great  possibilities  are  located  in  the  Juneau 
region;  a large  number  of  auriferous  lodes,  although  none  are  com- 
parable in  magnitude  with  those  of  the  better-known  properties  of 
the  Juneau  region,  are  massed  in  the  Berners  Bay  region — a com- 
paratively small  area — and  on  account  of  the  favorable  topographic 
conditions  make  that  region  an  attractive  mining  field. 

The  general  geologic  features  of  the  Juneau  gold  belt  as  a whole 
have  been  described  by  Spencer.®  During  his  reconnaissance  of  the 
gold  belt  in  1903  only  two  or  three  days  could  be  devoted  to  the 
Berners  Bay  region,  but  that  brief  study  sufRced  to  bring  out  the 
broader  facts  concerning  the  ore  bodies.  In  the  same  year  he  com- 
pleted a detailed  geologic  investigation  of  the  environs  of  Juneau 
and  was  able  to  publish  a geologic  map  on  the  scale  of  1 mile  to  the 
inch  to  accompany  his  report.  The  present  study,  undertaken  in 
the  year  1909,  is  part  of  the  plan  that  contemplates  a detailed  inves- 
tigation of  the  northern  portion  of  the  Juneau  gold  belt,  to  connect 
with  the  earlier  detailed  work  of  Spencer  in  the  vicinity  of  Juneau. 

Field  work  on  the  Berners  Bay  region  was  commenced  by  the 
writer  on  May  25,  1909,  and  completed  July  6,  1909.  The  condi- 
tions under  which  it  was  carried  on  were  not  of  the  most  auspicious 
character.  On  account  of  the  unusually  late  season  snow  lay  on 
the  mountains  above  an  altitude  of  1,000  feet  during  the  greater 

o Spencer,  A.  C.,  The  Juneau  gold  belt,  Alaska:  Bull.  U.  S.  Geol.  Survey  No.  287, 1906. 

7 


8 


THE  BERNERS  BAY  REGION,  ALASKA. 


part  of  the  time.  The  rocks  are  obscured  as  a rule  by  a dense  growth 
of  moss  and  other  vegetation,  and  exposures  are  rare  between  the 
shore  and  the  timber  line.  Nevertheless  it  is  believed  that  the 
broader  distribution  of  the  rock  types  is  indicated  with  sufficient 
accuracy  on  the  geologic  map  accompanying  this  report  (FI.  II). 
The  general  cessation  of  all  mining  activity  in  the  region,  the  absence 
of  everyone  familiar  with  the  underground  development,  and  the 
inaccessible  condition  of  many  of  the  mines  precluded  as  complete 
a study  of  the  economic  geology  as  might  otherwise  have  been 
possible. 

HISTORY. 

Gold  ore  lodes  were  first  discovered  in  the  Berners  Bay  region  in 
1886  or  1887.®  According  to  local  report  fioat  was  found  by  pros- 
pectors at  the  mouth  of  Sherman  Creek,  and  this  led  to  the  discovery 
of  ore  bodies  outcropping  in  the  upper  portion  of  the  drainage  area 
of  this  stream.  In  1890  a settlement  known  as  Seward  City  was 
started  on  the  shore  of  Lynn  Canal  at  the  mouth  of  Sherman  Creek, ^ 
and  enjoyed  an  ephemeral  prosperity  during  the  middle  of  the  last 
decade  of  the  nineteenth  century.  The  settlement,  now  nearly 
deserted,  is  known  as  Comet,  the  name  Seward  having  been  adopted 
by  an  important  town  on  Resurrection  Bay  on  Kenai  Peninsula. 

Between  1890  and  1900  five  stamp  mills  aggregating  80  stamps 
were  erected  in  the  region.  Owing  to  a variety  of  causes,  they  are 
now  all  idle.  In  1905  the  Berners  Bay  Mining  and  Milling  Company, 
which  controlled  one  of  the  most  productive  mines  in  the  region  and 
which  held  other  valuable  properties,  became  involved  in  financial 
and  legal  difficulties.  A protracted  litigation  ensued  which  extended 
through  a number  of  years,  and  final  adjudication  was  not  rendered 
until  near  the  close  of  1909.  It  was  reported  in  March,  1910,  in 
current  numbers  of  the  mining  periodicals  that  the  property  had 
been  sold  at  marshal’s  sale  for  $800,000  to  the  International  Trust 
Company,  of  Boston.  Development  of  the  ore  bodies  and  rehabili- 
tation of  the  plant  and  tramways  will  undoubtedly  soon  be  under- 
taken and  a period  of  increasing  production  may  be  anticipated. 

PRODUCTION. 

The  total  production  of  the  Berners  Bay  region  up  to  the  close  of 
1909  has  been  approximately  $1,100,000.  Two  mines,  the  Comet 
and  the  Jualin,  have  furnished  almost  the  entire  output.  The  largest 
output  for  any  single  year  was  that  of  the  year  preceding  June,  1895, 
when  the  Comet  mine  is  reported  to  have  yielded  over  $200,000.^ 

a Garside,  G.  W.,  Trans.  Am.  Inst.  Min.  Eng.,  vol.  21, 1893,  p.  822. 

b Alaska:  Eleventh  Census,  1893,  p.  234. 

c Becker,  G.  F.,  Eighteenth  Ann.  Kept.  U.  S.  Geol.  Survey,  pt.  3, 1897,  p.  77. 


THE  BERNERS  BAY  REGION,  ALASKA. 


9 


GEOGRAPHY. 

SITUATION  OF  THE  REGION. 

The  Berners  Bay  region,  which  takes  its  name  from  a sheet  of 
water  4 miles  wide  indenting  the  northeast  side  of  Lynn  Canal,  is 
situated  45  miles  northwest  of  Juneau,  the  capital  of  Alaska.  The 
term  Berners  Bay  region”  would  naturally  include  all  territory 
contiguous  to  the  bay,  but  for  the  purposes  of  this  report,  as  in  po})- 
ular  usage,  the  name  is  applied  to  the  long,  tapering  peninsula  and 
its  mountainous  background  that  lie  between  Berners  Bay  and  Lynn 
Canal  (fig.  1).  The  areal  extent  is  approximately  50  square  miles. 

The  region  is  easily  reached  by  water  from  Juneau.  Local  steamers 
plying  on  a weekly  schedule  between  Juneau  and  Skagway  call 


Figure  1.— Sketch  of  Berners  Bay  region. 

regularly  at  Comet,  on  Lynn  Canal,  which  is  the  only  settlement  in 
the  district.  Although  no  post-office  is  maintained  at  Comet,  a 
weekly  mail  service  is  furnished  by  the  Post-Office  Department. 

PHYSICAL  FEATURES. 

Berners  Bay,  which  was  named  by  Vancouver  in  1794,  is  a broad 
and  deep  indentation  from  Lynn  Canal,  in  latitude  58°  42'  north  and 
longitude  135°  west,  and  lies  between  Point  St.  Mary  on  the  north 
and  Point  Bridget  on  the  south.  The  head  of  the  bay  is  marked  by 
extensive  tidal  flats  formed  by  the  distributaries  of  Berners  River, 
which  enter  from  the  north,  and  by  other  large  streams  of  glacial 
origin,  which  enter  from  the  east  and  northeast.  Harbors  are  not 


10 


THE  BERNERS  BAY  REGION,  ALASKA. 

common  in  the  bay,  but  a bight  known  locally  as  the  Jualin  cove 
affords  safe  anchorage  for  large  craft. 

Lynn  Canal,  or  Lynn  Channel,  as  it  was  named  by  Vancouver, 
flanks  the  region  on  the  west.  Although  deep  water  can  be  found 
near  shore,  there  are  no  harbors  affording  protection  from  storms. 
Lynn  Canal  is  a magnificent  fiord,  6 miles  wide  here,  and  is  the  high- 
way of  all  commerce  entering  Alaska  and  the  Yukon  by  way  of 
Skagway. 

The  Berners  Bay  region  is  characterized  by  abrupt  topographic 
relief  (PI.  I).  The  northern  part  consists  of  a rugged  assemblage  of 
precipitous  peaks  which  rise  steeply  from  the  shore  of  Lynn  Canal 
to  heights  of  5,000  feet.  The  most  notable  of  these  form  a group 
known  as  Lions  Head  Mountain,  whose  serrate  profile  is  said  to  show, 
when  seen  from  Chatham  Strait,  a resemblance  to  a couch  ant  lion. 
Toward  the  south  the  altitudes  become  lower  and  the  profiles  of  the 
mountains  become  smoother  and  rounder,  until  near  the  tip  of  the 
peninsula  the  low  hills  scarcely  attain  an  altitude  of  500  feet. 

The  streams  on  the  peninsula  are  short,  but  on  account  of  the  heavy 
rainfall  they  carry  relatively  large  volumes  of  water.  Johnson  and 
Sherman  creeks  are  the  largest,  and  they  are  also  the  most  important 
because  of  the  fact  that  most  of  the  properties  are  located  in  their 
drainage  areas. 

Johnson  Creek  heads  in  an  amphitheater  of  ideal  symmetry  lying 
under  the  shadow  of  Lions  Head  Mountain  and  flows  southeastward 
through  a U-shaped  valley,  emptying  into  Berners  River  near  the  head 
of  the  tidal  flats  of  the  bay.  Its  total  length  is  only  4 miles.  The 
lower  course  is  broken  by  a waterfall  75  feet  high  and  affords  a favor- 
able site  for  the  development  of  hydroelectric  power. 

Sherman  Creek  is  a short  stream  heading  opposite  Johnson  Creek 
and  flows  northwestward  into  Lynn  Canal.  It  is  fed  by  numerous 
small  tributaries  cascading  from  the  high  mountains  that  flank  the 
stream  on  its  north  side.  Below  an  altitude  of  500  feet  Sherman 
Creek  is  intrenched  in  a narrow  gorge. 

CLIMATE  AND  VEGETATION. 

No  climatologic  data  concerning  the  Berners  Bay  region  are  avail- 
able, but  the  records  for  Juneau  and  Skagway  will  serve  to  give  a 
general  idea  of  the  climatic  conditions.  As  shown  by  the  subjoined 
table,  which  was  furnished  by  the  courtesy  of  the  Weather  Bureau, 
the  total  precipitation  is  considerably  less  at  Skagway  than  at  Juneau. 
Although  Berners  Bay  is  approximately  midway  between  these  two 
cities,  the  climatic  conditions  seem  to  be  closely  similar  to  those 
obtaining  at  Juneau. 


GEOGRAPHY. 


11 


Climatologic  data  for  Juneau  and  Sicagway,  Alaska. 

Mean  maximum  temperature. 


station. 

Jan. 

Feb. 

Mar. 

Apr. 

May. 

June. 

July. 

Aug. 

Sept. 

Oct. 

Nov. 

Dec. 

Annual. 

Juneau 

32.9 

34.3 

39.8 

47.6 

55.9 

62.7 

64.6 

61.4 

55.6 

48.3 

40.5 

35.9 

48.3 

Skagway 

24.9 

27.6 

35.8 

47.9 

60.7 

66.  7 

68.5 

64.1 

56.5 

46.1 

36.7 

31.3 

47.2 

Mean  minimum  temperature. 


Juneau 

24.2 

. 24. 2 28. 7 

34.8 

40.8 

46. 3!  49. 6 

48.2 

44.0 

38.1  30.3 

27.2  S 

Skagway 

15.9 

18.1  22.2 

32.4 

39.2 

46. 3 48. 2 

47.3 

. 

42.0 

35.8  28.5 

23. 3 3 

Mean  temperature. 


Juneau 

28.5 

29.3 

34.3 

41.2 

48.4 

54.5 

57.4 

54.8 

49.8 

43.2 

35.5 

31.9 

42.4 

Skagway 

20.5 

22.9 

29.0 

40.  1 

49.9 

56.5 

58.7 

55.7 

49.3 

40.9 

32.6 

27.3 

40.3 

Maximum  temperature. 


Juneau 

50 

51 

61 

63 

80 

84 

88 

82 

74 

68 

60 

60 

88 

Skagway 

47 

49 

63 

()2 

94 

90 

92 

89 

76 

63 

56 

57 

94 

Minimum  temperature. 


Juneau 

-10 

-4 

— 5 

13 

24 

31 

38 

36 

31 

20 

- 1 

1 

-10 

Skagway 

-21 

-9 

-•10 

9 

25 

33 

37 

31 

26 

12 

4 

- 4 

-21 

Mean  precipitation  (inches). 


Juneau 

7.87 

4. 75 

4.80' 

5.58 

5.40 

3.  97 

4.53 

7. 08 

11. 16 

10. 14 

8.54 

7.24 

Skagway 

1.20 

1.43 

.56 

1.78 

.68 

.90 

1. 13 

1.45 

2.65 

4. 76 

3.50 

2.76 

Mean  snowfall  (Inches). 


Juneau 

32. 9 23. 1 

11.7 

4.8 

0 

0 

0 

0 

0 

1.3 

6.6 

30.1 

110.5 

Skagway 

11.0  3.6 

1.2 

.9 

0 

0 

0 

0 

0 

2.8 

10.4 

12.2 

42.1 

Average  number  of  days  with  precipitation. 


Juneau 

17 

12 

14 

18 

16 

13 

14 

17 

20 

21 

19 

19 

200 

Skagway 

6 

4 

4 

7 

4 

5 

5 

7 

10 

14 

10 

9 

85 

Period  of  climatologic  records,  Alaska  stations. 

JiinGaur  Years. 

1890-1891 2 

1899-1908 ]0 

Total r 12 

Skagway:  1899-1908  (record  missing  from  September,  1900,  to  April,  1902) 8 


The  region  is  well  forested  with  spruce  and  hemlock.  The  timber 
line  (the  limit  of  erect  tree  growth)  reaches  2,500  feet  above  sea 
level  along  Lynn  Canal,  but  stands  several  hundred  feet  lower  on 
the  mountains  flanking  Berners  River  on  the  west;  In  most  places 


12 


THE  BERNERS  BAY  REGION,  ALASKA. 


a growth  of  low  contorted  forest  extends  a few  hundred  feet  above 
timber  line.  As  a rule,  the  timber  forms  open  stands,  and  the  largest 
and  finest  trees,  many  of  which  attain  a diameter  of  several  feet, 
are  found  in  the  alluvial  bottoms  bordering  Berners  River.  The 
undergrowth  is  rank  and  luxuriant  and  in  many  places  forms  impene- 
trable thickets.  Alder  and  devifs  club  are  particularly  common, 
but  many  other  kinds  of  shrubby  growth  occur. 

GLACIATION. 

A few  small  glaciers  are  left  in  the  region  and  their  distribution 
is  indicated  on  the  map  (PI.  I).  On  the  Lynn  Canal  side  they  have 
nearly  disappeared,  lying  only  in  the  amphitheaters  at  the  heads 
of  the  high  hanging  valleys.  On  the  Berners  River  side  they  are 
much  larger  and  descend  considerably  farther  from  the  gathering 
grounds — a difference  that  seems  to  be  due  to  the  diminished  insola- 
tion on  the  north  side  of  the  range. 

The  only  moraine  in  the  region  is  found  at  3,300  feet  elevation 
in  the  cirque  above  the  Ivanhoe  mine.  It  consists  of  blocks  of 
amygdaloid,  and  is  20  or  30  feet  high,  but  the  glacier  which  deposited 
it  has  retreated  from  it,  so  that  it  is  no  longer  in  process  of 
accumulation. 

During  the  recent  geologic  past  great  ice  streams  flowed  down 
the  troughs  of  Lynn  Canal  and  Berners  River  and  covered  the  larger 
part  of  the  region  under  ice.  Along  Lynn  Canal  diorite  erratics 
up  to  6 feet  in  diameter  were  found  east  of  Point  Sherman  at  an 
altitude  of  1,000  feet,  and  evidence  of  powerful  glacial  abrasion 
occurs  up  to  2,550  feet  above  sea  level.  Along  Berners  River 
roche  moutonnee  surfaces  persist  up  to  2,500  feet. 

In  general,  evidence  is  abundant  as  to  the  former  glacial  occupa- 
tion of  the  region,  but  observations  bearing  on  the  maximum  thick- 
ness of  the  trunk  glacier  that  formerly  occupied  Lynn  Canal  are 
not  so  readily  obtained.  The  data  at  hand  indicate  that  the  mini- 
mum thickness,  measured  from  present  sea  level,  was  2,600  feet; 
from  data  procured  south  of  Berners  Bay,  3,400  feet  appears  to  be  a 
maximum  measure  of  the  thickness  of  the  former  ice  mass. 

OUTLINE  OF  GEOLOGY  AND  ORE  DEPOSITS. 

The  sedimentary  rocks  of  the  Berners  Bay  area  consist  of  an 
interstratified  series  of  slates  and  graywackes,  named  the  Berners 
formation  because  it  is  well  exposed  across  the  strike  on  both  shores 
of  Berners  Bay.  The  formation  occupies  the  larger  part  of  the 
area  and  lies  between  the  high  mountains  and  Lynn  Canal.  The 
strata  have  been  intensely  folded,  but  as  a rule  strike  northwest 
and  southeast  and  dip  steeply  northeast.  Fossil  plants,  consisting 


OUTLINE  OF  GEOLOGY. 


18 


chiefly  of  ferns,  were  found  in  the  rocks  on  the  east  side  of  Beriuns 
Bay  and  indicate  that  the  formation  is  of  Jurassic  or  Lower  Cre- 
taceous age. 

A belt  of  much  altered  basic  lavas,  which  forms  Lions  Head  Moun- 
tain and  the  high  peaks  north  of  Independence  Creek,  extends 
northwestward  from  Berners  River  to  Lynn  Canal.  The  ancient 
volcanic  rocks  are  commonly  amygdaloidal  and  contain  numerous 
amygdules  of  epidote.  During  the  time  that  has  elapsed  since  the 
lavas  were  erupted  they  have  undergone  many  vicissitudes;  some 
which  originally  were  diabase  porphyries  now  resemble  fine  granular 
diorites,  owing  to  the  fact  that  the  pyrogenic  augite  has  been  con- 
verted to  fibrous  hornblende;  others  have  been  rendered  partly 
schistose,  forming  hornblende  schists,  and  subsequently  they  have 
been  recrystallized  around  the  borders  of  an  intrusive  mass  of  diorite. 
In  consequence  of  the  various  kinds  of  metamorphism  to  which 
they  have  been  subjected  their  originally  volcanic  character  is  in 
many  places  highly  obscure. 

Some  felsitic  or  rhyolitic  dikes  and  sills  occur  with  the  amygda- 
loids,  in  places  cutting  across  the  bedding  and  in  places  lying  between 
the  volcanic  sheets.  They  are  light-colored  rocks  of  dense,  flintlike 
texture,  and  weather  white  on  exposed  surfaces.  They  range  in 
thickness  from  a few  feet  to  about  100  feet. 

The  northeastern  part  of  the  region  is  underlain  by  quartz  diorite 
gneiss,  a part  of  the  granitoid  core  making  up  the  axial  mass  of 
the  Coast  Range.  On  the  west  side  of  Berners  Bay  the  gneiss  lies 
in  contact  with  the  amygdaloids;  on  the  east  side  it  intrudes  the 
rocks  of  the  Berners  formation.  At  some  time  after  its  intrusion 
the  quartz  diorite  was  rendered  coarsely  schistose  by  the  action  of 
powerful  stresses,  as  is  shown  by  the  partly  crushed  character  of  its 
component  minerals  when  viewed  under  the  microscope. 

A mass  of  diorite,  named  the  Jualin  diorite  because  it  is  well 
displayed  at  the  Jualin  mine,  occupies  the  basin  of  Johnson  Creek 
and  the  upper  portion  of  that  of  Sherman  Creek.  It  is  a grayish 
rock,  composed  essentially  of  plagioclase  feldspar,  hornblende,  and 
biotite,  and  ranges  in  texture  from  rather  fine  granular  to  coarse 
granular.  A small  area  of  heavy  black  rock  composed  mainly  of 
hornblende — a coarse  hornblendite — is  associated  with  this  variety 
of  diorite  near  Berners  River. 

The  Jualin  diorite  is  undoubtedly  of  younger  age  than  the  quartz 
diorite  gneiss  and  has  escaped  the  widespread  crushing  to  which  the 
older  rock  was  subjected.  It  is  intrusive  into  the  slates  and  gray- 
wackes  of  the  Berners  formation  and  into  the  series  of  basic  amyg- 
daloids. It  has  produced  some  contact  alteration  of  the  sedimentary 
rocks,  but  has  effected  more  profound  changes  in  the  volcanic  rocks, 
so  that  their  original  characteristics  are  locally  obliterated. 


14 


THE  BERNERS  BAY  REGION,  ALASKA. 


The  general  geologic  history  of  southeastern  Alaska  suggests  that 
the  irruption  of  the  quartz  diorite  and  the  Jualin  diorite  took  place 
during  one  broad  epoch  of  intrusion,  which  so  far  as  now  known 
extended  through  the  greater  part  of  the  Jurassic  period.  At  Berners 
Bay  powerful  deformational  forces  have  been  operative  between 
successive  intrusions. 

The  Jualin  diorite  is  the  most  important  rock  in  the  region  from  an 
economic  point  of  view.  The  main  ore  bodies,  in  both  point  of  size 
and  of  content,  lie  within  the  area  underlain  by  it. 

The  ore  bodies  are  auriferous  deposits,  of  which  the  larger  number 
are  either  well-defined  fissure  veins  or  irregular  stockwork  deposits. 
The  fissure  veins  range  up  to  15  feet  in  thickness,  but  the  average 
vein  is  5 feet  thick;  the  stockworks  range  up  to  80  feet  in  thickness. 
The  mineralogy  of  the  ores  is  exceedingly  simple ; the  gangue  material 
is  quartz  with  subordinate  calcite,  and  the  principal  metallic  sulphide 
is  pyrite  with  which  are  minor  amounts  of  chalcopyrite,  galena,  and 
sphalerite.  Gold  is  rarely  seen. 

The  wall  rock  of  the  ore  bodies  has  been  affected  by  a locally  intense 
hydrothermal  metamorphism,  the  characteristic  feature  of  which  is 
the  production  of  albite,  especially  in  the  small  veinlets  that  penetrate 
the  altered  wall  rock.  This  metamorphism  is  similar  to  that  in  the 
Juneau  region,  notably  like  that  which  has  transformed  the  Tread- 
well albite-diorite  dike  into  an  auriferous  lode.  The  ore  bodies  are 
therefore  of  deep-seated  origin,  and  a magmatic  source  for  the  vein- 
forming solutions  is  regarded  as  probable.  General  considerations 
indicate  that  the  deposits  are  likely  to  extend  downward  to  the  limits 
of  profitable  mining. 

During  the  recent  geologic  past  the  region  was  affected  by  a power- 
ful glacial  erosion,  so  that  the  ores  now  exposed  at  the  surface  are  of 
primary  origin. 

GENERAL  GEOLOGY. 

BERNERS  FORMATION  (JTJRASSIC-CRETACEOUS). 

GENERAL  CHARACTER  AND  DISTRIBUTION. 

A sedimentary  formation  consisting  predominantly  of  slates  and 
graywackes  occupies  the  largest  part  of  the  Berners  Bay  area.  Some 
basaltic  greenstones  and  quartz  porphyry  schists  are  associated  with 
it,  but  are  of  small  importance.  The  slates  comprise  in  the  main 
highly  cleaved  black  clay  slates,  but  include  some  of  green  and  to  a less 
extent  some  of  red  color.  The  graywackes  are  intimately  interstrati- 
fied  with  the  slates  in  beds  ranging  from  a few  inches  to  8 feet  or  more 
in  thickness,  and  are  commonly  of  a gray  or  greenish-gray  color. 
They  are  roughly  schistose  and  in  the  thicker  beds  nearly  massive. 

In  places  the  graywackes  constitute  the  bulk  of  the  formation  and 
comprise  a thick  succession  of  heavy  beds  separated  only  by  thin  beds 


GENERAL  GEOLOGY. 


15 


of  slate.  This  massive  development  of  graywacke  is  particularly 
well  shown  toward  the  south  end  of  the  peninsula. 

The  general  strike  of  the  rocks  is  northwest  and  southeast,  and  the 
dip  is  steep  to  the  northeast,  averaging  70°.  Locally  high  dips  to  the 
southwest  occur. 

The  rocks  of  this  formation  are  splendidly  displayed  along  the  west 
shore  of  Berners  Bay  and  along  Lynn  Canal  from  Point  St.  Mary  to 
the  mouth  of  Independence  Creek.  Topographically  they  form  the 
lower-lying  parts  of  the  region,  and  the  boundary  between  the  sedi- 
mentary slate  and  graywacke  formation  and  the  igneous  rocks  also 
separates  the  area  of  the  bold  craggy  peaks  from  the  lesser  moun- 
tains and  hills  that  make  up  the  southern  part  of  the  peninsula. 

The  formation  is  also  finely  exposed  on  the  east  shore  of  Berners 
Bay,  where  it  includes,  however,  an  important  series  of  augite  mela- 
phyres®  and  related  pyroclastic  rocks.  The  volcanic  member  attains 
its  main  development  as  a narrow  belt  fringing  the  shore  of  Lynn 
Canal  from  Auke  Bay  to  Point  Bridget  on  the  east  side  of  Berners  Bay. 
The  nonappearance  of  this  belt  on  the  west  side  'of  Berners  Bay  is 
probably  due  to  the  fact  that  the  strike  carries  it  to  the  west  of  Point 
St.  Mary. 

On  account  of  the  thick  carpet  of  moss  that  is  everywhere  prevalent 
below  timber  line  the  sedimentary  rocks  are  poorly  exposed  inland, 
and  the  internal  structure  of  the  formation  can  not  be  unraveled. 
In  the  shore  cliffs,  however,  it  can  be  seen  that  the  rocks  have  been 
profoundly  folded  and  closely  compressed,  and  that  the  axes  of  fold- 
ing have  also  been  acutely  folded,  and  that  in  places  they  pitch  verti- 
cally. In  consequence  of  this  severe  folding  of  the  axes  it  happens 
that  at  many  places  closely  adjacent  strata  show  an  angular  discord- 
ance of  strikes.  Ordinarily  this  would  be  taken  to  indicate  faults  of, 
some  magnitude,  but  along  the  beach,  where  the  geologic  relations  are 
perfectly  exposed,  it  can  be  seen  that  this  feature  is  due  to  the  vertical 
attitude  of  nearly  appressed  folds. 

Subsequent  to  the  complex  folding  of  the  rocks  a cleavage  was 
induced  in  them,  which  commonly  coincides  with  the  stratification 
and  trends  N.  45°  W.  (true).  In  places,  such  as  in  the  arches  of  those 
folds  which  are  standing  on  edge,  the  cleavage  is  conspicuously 
across  the  bedding.  The  cleavage,  therefore,  rather  than  the  strati- 
fication, is  the  most  constant  structural  feature  of  the  formation. 

An  enormous  amount'  of  quartz  veining  in  the  form  of  stringers 
following  the  foliation  of  the  rocks  has  affected  the  slates  and  gray- 
wackes,  but  the  amount  of  pyritic  mineralization  of  these  veinlets 
is  nearly  insignificant. 


a This  term  is  used  in  a purely  descriptive  sense,  as  advocated  by  rirsson  in  “ Rocks  and  rock  minerals.’”' 


16 


THE  BERNERS  BAY  REGION,  ALASKA. 


PETROGRAPHY. 

The  graywackes  typical  of  the  region  consist  of  gray  or  greenish- 
gray  rocks  in  which  none  of  the  mineral  constituents  are  discrimi- 
nable  by  the  eye.  Some,  however,  contain  innumerable  small  frag- 
ments of  black  slate,  and  isolated  beds  are  found  that  contain  angular 
fragments  of  slate  several  inches  long.  A more  or  less  thorough 
schistosity  has  been  impressed  upon  the  graywackes,  the  perfection 
of  which  increases  as  a rule  with  the  thinness  of  the  beds  and  the 
fineness  of  grain  of  the  component  materials.  Some  of  the  more  highly 
foliated  varieties  can  not  be  distinguished  by  the  eye  from  sheared 
igneous  rocks. 

Under  the  microscope  the  graywackes  are  found  to  consist  largely 
of  altered  fragments  ^of  plagioclase,  some  of  which  is  referable  to 
AbyAng,  embedded  in  an  argillaceous  matrix  which  is  somewhat 
chloritic.  The  entire  absence  of  quartz  in  typical  graywackes  taken 
from  several  localities — the  mouth  of  Independence  Creek,  Jualin 
Cove,  and  others — is  rather  remarkable.  Many  of  the  feldspar 
fragments  are  partly  bounded  by  crystallographic  outlines  and  show 
rounded  corners  ; others  are  highly  angular.  Fragments  of  andesitic 
rock  and  slivers  of  slate  and  possibly  other  sedimentary  rock  are  of 
occasional  occurrence.  Numerous  fragments  of  augite  are  present 
in  the  rock  from  Jualin  Cove,  and  in  the  graywackes  on  the  east  side 
of  Berners  Bay  this  mineral,  or  what  appears  to  be  its  metamorphic 
equivalent,  fibrous  hornblende,  occurs  in  quantities  appreciable  to 
the  eye.  Other  minerals  found  in  subordinate  amounts  are  calcite, 
epidote,  hornblende,  pyrite,  magnetite,  and  apatite.  In  certain  beds, 
however,  calcite  becomes  an  important  constituent. 

The  slates  require  no  particular  description.  Black  or  bluish-black 
clay  slates  predominate.  Locally,  as  in  the  gorge  of  Sherman  Creek, 
they  are  characterized  by  a brilliant  black  luster  due  to  the  presence 
of  finely  disseminated  graphite.  Slates  of  green  color  are  found  in 
small  amounts  at  many  places  throughout  the  region,  and  are 
particularly  well  exposed  on  both  sides  of  Berners  Bay.  They  are 
more  massive  and  less  fissile  than  the  black  slates. 

A rock  of  somewhat  marked  individuality  belonging  to  the  class 
of  graywacke  slates  has  a scanty  distribution  in  the  Berners  Bay 
region  but  becomes  increasingly  prominent  as  a member  of  this 
formation  in  its  extension  to  the  southeast,  and  therefore  deserves 
mention  here.  In  its  general  aspect  this  rock  resembles  a black  clay 
slate,  but  differs  from  that  in  containing  numerous  small  augen  of 
quartz  and  of  a black  glassy  cleavable  mineral,  the  presence  of  the 
augen  producing  a porphyritic  effect.  In  thin  section  the  black 
glassy  mineral  proves  to  be  a feldspar  whose  color  is  due  to  the  infil- 
tration of  carbonaceous  material.  The  quartz  is  seen  to  show  strong 


GENERAL  GEOLOGY. 


17 


undulatory  extinction.  These  two  constituents  rest  in  a thoroughly 
schistose  matrix  of  chlorite,  quartz,  and  carbonaceous  matter, 
throughout  which  is  scattered  a small  amount  of  accessory  pyrite. 

AGE  AND  CORRELATION. 

This  formation  was  regarded  by  Spencer  as  the  northwestern 
extension  of  the  slate-greenstone  band  of  the  Juneau  region,  and  on 
account  of  the  presence  of  fossils  found  in  intercalated  limestones 
at  Taku  Harbor,  which  is  25  miles  southeast  of  Juneau,  was  believed 
to  be  of  Carboniferous  age.  ' 

Some  fossil  plants  were  collected  during  the  present  investigation 
from  the  east  side  of  Berners  Bay  just  north  of  Sawmill  Cove.  The 
rocks  here  consist  of  an  interdigitating  series  of  thick  lenses  of  gray- 
wacke  and  argillite  standing  on  edge.  The  graywackes  show  cross- 
bedding  and  the  argillites  are  ripple  marked.  The  argillaceous  rocks 
are  as  a rule  too  highly  cleaved  to  have  retained  the  imprints  of  leaves, 
which  are  now  commonly  represented  by  graphitized  flakes.  Leaf- 
bearing beds  seem  to  be  scarce,  and  the  best  fossils  collected  were 
obtained  from  a roughly  schistose  argillite  which  was  gashed  by 
quartz  veinlets.  F.  H.  Knowlton,  of  the  United  States  Geological 
Survey,  reports  on  the  plants  as  follows: 

This  material  is  very  difficult  to  study,’ for  practically  all  traces  of  nervation  are 
absent  and  dependence  must  be  placed  on  outline,  which  has  obviously  been  more 
or  less  modified  by  pressure.  With  these  limitations  in  mind,  I think  I have  been 
able  to  demonstrate  the  presence  of  Taen  iopteris,  Asplenium  or  Dicksonia,  Thinnfeldia{"^) 
and  possibly  another  fern  something  like  Dryopteris. 

The  choice  appears  to  lie  between  Jurassic  and  Lower  Cretaceous,  and  if  what  has 
been  supposed  to  be  Tseniopteris  is  really  such  the  odds  favor  the  former.  I have 
not  found  anything  that  can  be  identified  as  a dicotyledon,  which  also  is  favorable 
to  the  probability  of  its  being  Jurassic.  Although  the  evidence  as  adduced  is  not 
very  strong  and  the  identifications  are  tentative,  it  seems  most  probable  that  they 
are  of  Jurassic  age. 

According  to  this  determination  the  rocks  of  the  Berners  Bay 
region  are  to  be  correlated  in  an  approximate  way  with  the  Aucella- 
bearing  terrane  found  by  C.  W.  Wright  on  Admiralty  Island.® 
This  is  regarded  as  of  Lower  Cretaceous  or  possibly  Upper  Jurassic 
age.  The  lithology  is  described  as  including  conglomerates,  gray- 
wackes, and  slates.  The  Admiralty  Island  rocks  were  probably  laid 
down  subsequent  to  the  intrusion  of  the  Coast  Range  diorites,  though 
this  is  a moot  point  in  the  geology  of  southeastern  Alaska;  the  rocks 
of  the  Berners  Bay  region  are  predioritic.  The  invasion  of  the  prov- 
ince by  the  plutonic  masses  of  the  Coast  Range  is  the  most  important 
event  in  the  geologic  history  of  the  region,  and  the  determination  of 
the  exact  stratigraphic  relations  existing  between  these  two  terranes 
is  therefore  a problem  of  prime  importance. 

a Bull.  U.  S.  Geol.  Survey  No.  287,  1906,  p.  144. 

G7811°— Bull.  446—11 2 


18 


THE  BERNERS  BAY  REGION,  ALASKA. 


DIKES. 

Under  this  heading  are  described  various  minor  bodies  of  igneous 
rock  of  widely  diverse  characters  that  occur  within  the  area  of  the 
slates  and  graywackes.  The  diorite  porphyry  dikes  that  are  found 
as  offshoots  from  the  main  mass  of  the  Jualin  diorite  are  not  discussed 
here. 

In  a prospect  trench  dug  in  the  boss  in  the  lower  part  of  the  valley 
of  Johnson  Creek  is  exposed  a quartz  porphyry  schist.  The  relation 
to  any  incasing  rocks  is  effectually  concealed  under  a growth  of 
moss.  The  quartz  porphyry  schist  is  a thoroughly  foliated  rock  of 
light-greenish  color  and  of  oily  appearance.  On  joint  age  sur- 
faces cutting  across  the  schistosity  can  be  seen  numerous  quartzes, 
more  or  less  bounded  by  crystal  faces,  resting  in  a dense  matrix. 
Rocks  of  this  character  were  not  observed  elsewhere  in  the  region, 
nor  have  they  been  previously  noted  in  the  Juneau  gold  belt.  Under 
the  microscope  some  of  the  quartz  phenocrysts  prove  to  be  character- 
istically embayed,  and  this  feature  affords  a most  convincing  criterion 
of  the  originally  igneous  character  of  the  rock.  Feldspar  phenocrysts 
occur  but  are  obscure ; epidote  pseudomorphs,  apparently  after  horn- 
blende, are  found.  These  constituents  are  embedded  in  a highly 
schistose  matrix  of  sericite  and  quartz.  Titanite  in  typical  wedge 
forms  is  a fairly  abundant  accessory,  and  apatite,  in  unbroken  prisms 
where  lying  in  the  lee  of  phenocrysts,  is  of  sporadic  occurrence  and 
is  especially  common  in  the  epidote  pseudomorphs.  Calcite,  pyrite, 
and  tourmaline  are  present  in  small  amounts. 

Some  thin  dikes  of  lamprophyric  character  are  occasionally  found. 
Two  were  noted  injected  parallel  to  the  stratification  along  the  shore 
of  Lynn  Canal  near  the  mouth  of  Independence  Creek.  They  are 
dark,  heavy  rocks,  rudely  schistose,  and  the  dikes  show  dense  cliilled 
borders.  Numerous  crystals  of  augite  constitute  the  sole  pheno- 
crystic  constituent;  abundant  idiomorphic  augite,  though  the  indi- 
vidual crystals  are  not  of  uniform  size,  occurs  in  the  groundmass. . 
Some  laths  of  highly  pleochroic  biotite  and  a little  brown  idiomorphic 
hornblende  appear  also,  and  labradorite  forms  an  interstitial  filling. 
Magnetite  is  present  as  an  accessory,  and  calcite,  chlorite,  and  pyrite 
are  secondary  minerals. 

On  the  east  side  of  Berners  Bay  one  of  these  lamprophyric  dikes 
was  noted  which  seemingly  consists  mainly  of  pyroxene  phenocrysts. 
Under  the  microscope,  however,  it  was  found  that  the  pyroxene  had 
been  completely  transformed  into  fibrous  amphibole,  typical  pyroxene 
cross  sections  showing  pleochroism  and  characteristic  amphibole 
cleavage.  The  original  character  of  the  groundmass  is  undecipher- 
able from  the  new  growth  of  amphibole  and  calcite. 

North  of  the  Portland  mill  on  the  shore  of  Lynn  Canal  a dike  of 
diorite  porphyry  50  feet  thick  is  well  exposed.  This  rock  is  rendered 


GENERAL  GEOLOGY. 


19 


highly  porphyritic  by  the  presence  of  numerous  prisms  of  hornblende, 
ranging  in  length  from  1 inch  down;  no  other  phenocrysts  are  present. 
The  matrix  is  gray  in  color  and  aphanitic  in  texture ; microscopically 
it  proves  to  consist  mainly  of  much  altered  plagioclase. 

BASIC  VOLCANIC  ROCKS. 

GENERAL  CHARACTER  AND  DISTRIBUTION. 

A series  of  ancient  lavas,  mainly  of  basaltic  character,  form  a belt 
trending  northwestward  from  Berners  Kiver  to  Lynn  Canal.  These 
old  volcanic  rocks  make  up  the  mountainous  mass  known  as  the  Lions 
Head  and  form  the  precipitous  peaks  flanking  Lynn  Canal  north  of 
Independence  Creek.  Brown,  red,  greenish-blue,  and  other  dark 
hues  are  the  prevailing  colors.  As  a rule  the  rocks  are  conspicuously 
spotted  with  yellowish-green  amygdules  of  epidote,  and  as  this  is  in 
places  their  most  prominent  feature  they  may  conveniently  be  called 
epidotic  amygdaloids.  Sporadically  the  amygdules  carry  a small 
amount  of  chalcopyrite. 

This  volcanic  series  consists  almost  wholly  of  a superposed  succes- 
sion of  lava  flows.  Intercalated  sheets  of  breccia  were  observed  at 
only  one  locality.  The  bedded  character  is  commonly  obscure,  but 
occasionally  sheets  differing  in  color  and  texture  can  be  found  in 
juxtaposition.  These  contacts  may  in  places  be  rendered  conspicuous 
by  the  highly  amygdaloidal  character  of  the  marginal  portion  of  one 
or  the  other  of  the  lava  sheets.  In  such  places  the  structure  can  be 
determined,  and  where  thus  measured  it  is  found  to  strike  northwest 
and  southeast  and  to  dip  70°  N.,  coinciding  therefore  with  the  general 
structural  trend  of  the  region. 

In  places  the  rocks  exhibit  a rough  schistosity,  which  is  best  de- 
veloped near  the  quartz  diorite  gneiss  bordering  them  on  the  north- 
east. There  they  approach  hornblende  schists  in  structure  and  com- 
position. The  schistosity  coincides  in  direction  with  the  bedding. 

PETROGRAPHY. 

A 

Some  variation  in  the  appearance  of  the  basalts  is  noticeable  from 
place  to  place,  but  on  the  whole  the  differences  are  mainly  due  to 
the  different  kinds  of  metamorphism  to  which  the  various  rocks 
have  been  subjected. 

The  basalts  so  well  exposed  along  Lynn  Canal  north  of  Independ- 
ence Creek  are  dark  greenish-gray  rocks,  nonporphyritic  and  fine 
textured.  They  are  highly  amygdaloidal,  epidote  being  most  com- 
monly distinguishable  as  the  filling  of  the  vesicles,  and  quartz  more 
rarely.  Microscopically  they  prove  to  be  plagioclase-augite  rocks  of 
doleritic  texture.  Little  or  none  of  the  augite  has  escaped  altera- 
tion to  epidote  and  chlorite,  and  the  numerous  amygdules  that  occur 
throughout  the  rock  are  filled  with  the  same  minerals. 


20 


THE  BERNERS  BAY  REGION,  ALASKA. 


Kock  taken  above  the  Ivanhoe  mine  at  an  altitude  of  3,100  feet 
is  coarser  textured  and,  on  account  of  the  abundance  of  ferromag- 
nesian  mineral  in  it,  resembles  a dark-colored  fine-granular  diorite. 
It  contains  scattered  amygdules  of  epidote.  Under  the  microscope 
large  sporadic  phenocrysts  of  plagioclase  are  found  to  lie  embedded 
in  a coarse  ophitic  matrix,  but  instead  of  augite  brown  amphibole 
appears.  This  amphibole  occurs  also  in  tufts  and  irregular  aggre- 
gates of  fibers  in  the  feldspars,  and  the  ends  of  the  large  hornblendes 
fray  out  in  bundles  of  diverging  prisms.  Granular  epidote  is  com- 
monly associated  with  the  amphibole.  These  features  clearly  indi- 
cate the  derivative  origin  of  the  amphibole  and  show  that  the  rock 
was  originally  a vesicular  diabase  porphyry. 

Rocks  of  this  character  are  the  prevalent  variety  in  the  region. 
Toward  the  northeast,  as  already  stated,  they  take  on  a schistose 
structure,  and  the  microscopic  diagnosis  is  as  a rule  insufficient  to 
establish  their  volcanic  character.  The  field  evidence,  however,  is 
conclusive  on  this  point. 

Certain  rocks  from  Independence  Gulch  prove  to  be  amygdaloidal 
andesites.  They  carry ^ numerous  small,  rather  inconspicuous  feld- 
spar phenocrysts  in  a groundmass  which  is  of  denser  texture  than 
that  of  the  basalts.  The  multitude  of  yellowish-green  amygdules  is 
the  most  striking  feature  of  the  rocks.  The  feldspar,  when  examined 
optically,  proves  to  be  andesine;  the  groundmass  consists  of  forked 
feldspar  microlites  embedded  in  a decomposed  glassy  base.  The 
amygdules  are  Idled  with  epidote  and  subordinate  chlorite. 

CONTACT-ALTERED  PHASES. 

The  amygdaloids  have  been  invaded  by  the  Jualin  diorite  and 
considerable  changes  have  been  produced  in  them  around  the  bor- 
ders of  the  intrusion.  These  changes  consist  mainly  of  a recr3^stal- 
lization,  during  which  the  grain  of  the  volcanic  rock  has  become  suf 
ficiently  coarse  to  be  perceptible  to  the  eye.  The  metamorphism  is 
most  pronounced  in  those  places  where  the  rock  is  pierced  by  dikelets, 
and  the  resulting  product  may  resemble  a hornblende-rich  diorite. 
In  places  the  intrusive  diorite  has  caught  up  fragments  of  the  basalts 
and  has  recrystallized  and  partly  dissolved  them,  so  that  a most 
heterogeneous  sort  of  rock  has  been  produced  which  is  of  verj"  erratic 
composition  and  appearance.  These  features  are  particular! 3^  well 
shown  between  the  upper  and  lower  workings  of  the  Kensington 
mine. 

In  general  the  principal  effect  has  been  to  produce  a rock  in  which 
hornblende  is  the  most  abundant  constituent.  The  structure  is  that 
t3"pical  of  contact-metamorphic  rocks;  the  larger  mineral  individ- 
uals show  a spongiform  development,  and  droplike  particles  of  one 
mineral  are  commonly  included  in  the  other.  The  fibrous,  weakly 


GENERAL  GEOT.OGY. 


21 


pleochroic  amphibole  has  been  converted  into  a compact,  strongly 
pleocliroic  brown-green  hornblende;  the  feldspar,  wliich  is  com- 
monly subordinate,  is  clear,  glassy,  and  largely  unstriated,  and 
ranges  from  AbgyAngg  to  Ab6oAn4Q.  Magnetite  is  relatively  abundant. 
In  some  rocks  biotite,  which  nowhere  in  the  region  is  a pyrogenetic 
constituent  of  the  basalts,  is  developed  as  a product  of  contact 
metamorphism. 

AGE. 

The  contact  between  the  bedded  volcanic  rocks  and  the  Berners 
formation  is  hidden  by  vegetation  and  talus  slopes,  so  that  no  infer- 
ences as  to  the  relative  ages  of  the  rocks  could  be  drawn.  Other 
lines  of  evidence  must  be  used.  An  area  of  basaltic  greenstone  of 
obscurely  amygdaloidal  character  surrounded  by  slates  and  gray- 
wackes  occurs  on  the  south  side  of  Sherman  Creek,  as  shown  on 
Plate  I.  Other  such  areas  may  possibly  be  found,  but  on  account  of 
the  poor  exposures  and  dense  vegetation  no  attempt  was  made  to 
delimit  them.  Although  the  contacts  were  not  seen,  the  amygda- 
loidal character  suggests  that  the  rock  is  an  intercalated  flow  or 
series  of  flows,  and  inasmuch  as  it  is  lithologically  similar  to  the  rocks 
of  tlie  volcanic  belt  of  metabasalts,  the  conclusion  seems  to  follow 
that  all  are  essentially  of  the  same  age,  probably  Jurassic.  The 
only  fact  apparently  not  in  harmony  with  this  conclusion  is  that  fhe 
augite  melaphyres,  which  clearly  form  an  integral  portion  of  the 
Berners  formation  on  the  east  side  of  the  bay,  are  petrographically 
different  from  the  epidotic  amygdaloids.  This  difference  may  be 
due  to  the  fact  that  tliese  two  A^olcanic  members  represent  different 
eruptive  periods  during  the  accumidation  of  the  sedimentary 
formation. 

INTRUSIVE  FELSITES. 

Some  felsitic  dikes  and  sills  were  found  associated  with  the  amyg- 
daloids. They  are  aphanitic  flintlike  rocks  weathering  white  on 
exposed  surfaces,  and  some  show  a well-developed  flow  banding. 
Minute  quartzes  form  the  main  porphyritic  constituent,  but  as  a rule 
are  detected  only  with  difficulty.  Microscopically  the  rock  shows 
embayed  quartzes  and  small  sporadic  plagioclase  feldspars  resting  in 
a cryptocrystalline  groundmass  in  which  there  is  scattered  a little 
flaky  biotite,  some  magnetite,  and  accessory  zircon. 

The  intrusive  rocks  range  in  thickness  from  a few  feet  to  100  feet 
and  are  massive  even  where  intercalated  between  schistose  amygda- 
loids. Similar  rocks  are  known  to  occur  in  the  vicinity  of  Skagway, 
40  miles  north  of  Berners  Bay,  where  they  are  associated  with  a pink 
quartzose  granite  that  is  intrusive  into  quartz  diorite.®  They  are 
therefore  tentatively  considered  to  be  the  youngest  rocks  in  the 
Berners  Bay  area. 


a Information  from  L.  M.  rrindle. 


22  THE  BERNERS  BAY  REGION,  ALASKA. 

QUARTZ  DIORITE  GNEISS. 

GENERAL  CHARACTER. 

The  northern  part  of  the  Berners  Bay  region  is  occupied  by  quartz 
diorite,  which  nnakes  up  the  mountains  on  both  sides  of  Berners 
Kiver  and  extends  as  far  as  the  eye  can  see  into  the  glacial  fastnesses 
of  the  Coast  Range.  It  is  a rock  mass  of  uniform  character  except 
along  the  zone  bordering  the  contact.  A coarsely  schistose  or 
gneissic  structure  has  been  developed  in  the  quartz  diorite,  trending 
N.  40°  W.  (true)  and  dipping  steeply  to  the  northeast,  and  coincides 
thus  in  direction  with  the  cleavage  displayed  by  the  slates  and  gray- 
wackes.  The  quartz  diorite  gneiss  breaks  parallel  to  the  structure 
in  thick  tabular  blocks,  and  in  distant  views  presents  the  appearance 
of  a stratified  formation.  It  maintains  its  petrographic  character 
and  gneissic  structure  for  many  miles  to  the  southeast  of  Berners  Bay 
and  forms,  in  local  parlance,  the  hanging  wall  of  the  Juneau  gold  belt. 

PETROGRAPHY. 

The  quartz  diorite  gneiss  is  a granitoid  rock  of  medium  to  coarse 
grained  texture,  consisting  macroscopically  of  plagioclase,  quartz, 
biotite,  hornblende,  and  sporadic  crystals  of  titanite.  The  feldspars 
range  from  3 to  5 millimeters  in  diameter.  The  foliated  structure  is 
readily  apparent  in  hand  specimens.  Under  the  microscope  the 
texture  is  seen  to  be  hypidiomorphic  granular  modified  by  cataclastic 
phenomena.  The  plagioclase  approximates  Ab6oAn4o,  but  the  average 
composition  of  the  feldspar  is  difficult  to  determine  accurately  on 
account  of  the  strongly  developed  zonal  banding.  On  a section 
parallel  to  the  brachypinacoid  it  was  found  that  the  large  core  was 
Ab57Aii43;  this  was  succeeded  by  zones  alternately  more  sodic  and 
more  calcic,  though  all  were  more  sodic  than  the  core;  the  narrow 
zone  next  to  the  outermost,  however,  was  Ab5iAn4g  and  the  broad 
outermost  zone  AbegAngg.  The  feldspars  are  somewhat  granulated 
peripherally.  Quartz  forms  crushed  and  elongated  areas  composed 
of  interlocking  grains  which  show  strain  shadows.  Biotite  and  horn- 
blende, sliced  and  wrapping  around  the  feldspars,  constitute  the  dark 
minerals.  Orthoclase  is  present  in  insignificant  amounts  or  is 
entirely  absent.  Titanite,  apatite,  and  magnetite  occur  as  accessory 
minerals,  and  secondary  epidote,  chlorite,  and  sericite  are  present  in 
small  amounts. 

A typical  specimen  of  the  quartz  diorite  gneiss,  taken  at  a distance 
of  over  a mile  from  the  contact,  was  measured  according  to  BosiwaFs 
method,  the  traverses  being  run  across  the  structure,  in  order  to 
obtain  an  approximate  quantitative  measure  of  the  mineral  com- 
position. The  following  percentage  composition  by  weight  was 
obtained ; 


GENEEAL  GEOLOGY. 


23 


Mineral  rnmposif.ion  of  quartz  fliorile  gneiss^  Berners  Bag  region,  AJasha 


Plagioclase  (AbeoAn^o') 

Orthoclase 

Quartz 

Biotite 

Hornblende 

Titanite 

Apatite 

Chlorite 

Epidote. 

Sericite 


51.  1 
1.0 
25.0 
13.6 
4.8 
1. 1 
.1 
1.  9 
.8 
.6 

100.0 


This  composition  is  closely  similar  to  that  determined  for  the 
average  Coast  Range  intrusive  rock  in  the  Ketchikan  region  ® and  is 
characterized  by  the  same  unusual  percentage  of  titanite. 


CONTACT  PHENOMENA  AND  AGE. 


The  quartz  diorite  gneiss  shows  various  modifications  along  its 
contact  with  the  rocks  that  it  has  invaded.  On  the  east  side  of 
Berners  Bay  the  gneiss  includes  for  thousands  of  feet  from  the  contact 
vast  numbers  of  rock  fragments  and  detached  masses  of  stratified 
sediments,  which  show  a crumpling  in  conformity  with  the  structure 
of  the  rock  inclosing  them.  These  inclusions  were  highly  meta- 
morphosed— a fact  of  which  muscovite,  on  account  of  its  absence  in 
the  truly  igneous  rock,  is  the  most  notable  token — and  were  partly 
dissolved,  so  that  it  is  in  places  impossible  to  distinguish  between 
original  diorite  and  altered  sedimentary  rock.  Near  the  main  con- 
tact the  gneiss  becomes  finer  textured  and  deficient  in  femic  minerals. 
At  other  points,  however,  the  gneiss  becomes  richer  in  biotite  at 
the  contact,  and  in  consequence  takes  on  a more  thoroughly  foliated 
structure  than  ordinarily  prevails  throughout  the  main  mass.  A 
peculiar-looking  rock  results,  which  consists  of  numerous  aiigen  of 
feldspar  embedded  in  a foliated  groundmass  of  biotite  and  horn- 
blende. Under  the  microscope  the  feldspars  prove  to  be  AbjAn^; 
the  augen  effect  is  seen  to  be  due  to  the  fact  that  corners  of  the 
feldspars  have  been  rounded  off  by  peripheral  granulation.  Biotite 
and  hornblende,  both  sliced,  envelop  the  feldspars.  Titanite  (much 
of  which  is  crushed  and  dispersed),  apatite,  and  magnetite  occur  as 
accessory  minerals.  The  basic  character  of  this  marginal  phase  is 
therefore  expressed  by  the  greater  prevalence  of  femic  minerals, 
by  the  more  calcic  composition  of  the  feldspar,  and  by  the  absence  of 
quartz.  This  phase  of  the  gneiss  does  not  occur  along  the  contact 
with  the  sedimentary  rocks,  but  only  in  places  along  the  amygdaloids. 


a Wright,  F.  E.  and  C.  W.,  Bull.  U.  S.  Geol.  Survey  No.  347,  1908,  p.  04. 


24 


THE  BERNERS  BAY  REGION,  ALASKA. 


The  contact  relations  clearly  prove  the  intrusive  nature  of  the 
quartz  diorite  gneiss.  The  age  indicated  is  therefore  post-Jurassic 
or  post  Lower  Cretaceous.  The  quartz  diorite  gneiss  of  the  Berners 
Bay  region  is  part  of  the  composite  batholith  of  granitoid  rocks  that 
form  the  core  of  the  Coast  Range.  Spencer  showed  that  in  the 
Juneau  region  the  period  of  intrusion  was  post-Carboniferous  and 
argued  that  it  was  subsequent  to  the  deposition  of  the  Lower  Cre- 
taceous rocks  on  Admiralty  Island  and  before  the  Upper  Cretaceous 
strata  were  laid  down.®  The  Wright  brothers,  with  the  same  evidence 
before  them,  concluded  that  the  intrusions  are  of  pre-Cretaceous 
Mesozoic  age  and  continued  at  least  to  late  middle  Jurassic  time.^ 
More  detailed  work  is  needed  to  fix  the  ])criod  of  intrusion  with  a 
higher  degree  of  finality. 

JTJALIN  DIORITE. 

' GENERAL  CHARACTER  AND  OCCURRENCE. 

The  Jucthn  diorite  is  economically  the  most  important  lithologic 
unit  in  the  region.  It  occupies  the  drainage  area  of  Johnson  Creek 
and  the  upper  part  of  that  of  Sherman  Creek,  and  most  of  the  aurifer- 
ous lodes  are  located  within  the  confines  of  this  area.  The  number 
of  lodes  is  large  compai|ed  to  the  size  of  the  area,  and  the  diorite  has 
consequently  been  subjected  to  the  attack  of  vein-forming  solutions. 
Its  minerals  have  therefore  undergone  more  or  less  alteration,  and  the 
diorite  tends  to  assume  a greenish  color,  contrasting  in  this  respect 
with  the  fresh,  unaltered  appearance  of  the  quartz  diorite  gneiss. 
This  alteration  is  especially  noticeable  in  the  narrow  northwest  end 
of  the  diorite  area,  where  the  massing  of  ore  bodies  is  greatest. 

The  intrusion  of  the  Jualin  diorite  has  produced  some  contact- 
metamorphic  alteration  of  the  slates  and  graywackes,  but  this  change 
is  comparatively  small  in  extent.  Perceptible  changes  up  to  several 
hundred  feet  from  the  contact  have  been  brought  about  in  the  meta- 
basalts, as  already  described. 

Dikes  or  offshoots  from  the  main  mass  of  diorite  are  found  at 
various  places  along  the  contact.  They  differ  somewhat  in  appear- 
ance from  the  granular  diorite,  being  diorite  porphyries,  and  consist  of 
closely  packed  phenocrysts  of  plagioclase  and  some  hornblende  in  a 
dense  blue  matrix. 

PETROGRAPHY. 

The  Jualin  diorite  is  a granular  rock,  consisting,  so  far  as  the  eye 
can  determine,  of  plagioclase  feldspar,  hornblende,  and  biotite.  It 
varies  from  place  to  jilace  both  in  mineral  composition  and  in  texture. 
Hornblende  is  the  most  prevalent  dark  mineral,  but  locally  biotite 


a Bull.  U.  S.  Geol.  Survey  No.  287,  1906,  p.  19. 
b Bull.  U.  S.  Geol.  Survey  No.  347,  1908,  p.  76. 


GENERAL  GEOLOGY. 


25 


exceeds  it  in  prominence  and  in  other  ])laces  fails  entirely.  Tex- 
turally  the  diorite  ranges  from  finely  granular,  as  at  Jualin,  to  coarsely 
granular,  as  at  the  Kensington  mine.  As  seen  in  thin  section,  the 
diorite  displays  a hypidiomorphic  granular  structure.  The  plagio- 
clase  feldspar  is  a labradorite  near  AbjAn^  in  composition  and  shows 
idiomorphic  development.  Hornblende  and  biotite  are  the.  ferro- 
magnesian  minerals.  Allotriomorphic  orthoclase  and  interstitial 
quartz  are  present  in  subordinate  amounts,  although  at  certain 
localities,  as  at  the  Jualin  mine,  they  are  sufficiently  abundant  to 
cause  the  rock  to  approach  a granodiorite  in  composition.  Magnetite, 
titanite,  and  apatite  occur  as  accessory  minerals.  Secondary  alter- 
ation products,  such  as  epidote,  chlorite,  calcite,  and  sericite,  are 
everywhere  prevalent. 

The  Jualin  diorite  is  as  a rule  a massive  rock  unaffected  by  the 
parallel  structure  exhibited  by  the  quartz  diorite  gneiss.  Locally, 
as  adjoining  certain  quartz  veins,  the  diorite  has  been  reduced  to  a 
schist,  and  at  a number  of  localities  there  occur  what  are  locally 
designated  ‘‘slate  dikes.”  This  misnomer  is  perhaps  sufficiently 
descriptive  of  their  physical  appearance.  The  center  of  one  of  the 
“dikes”  which  is  about  30  feet  thick  consists  of  black,  closely 
foliated  schist;  laterally  this  schist,  by  progressively  wider  spacing 
of  the  foliation  planes,  grades  into  the  undeformed  diorite  country 
rock.  The  black  schist,  when  examined  microscopically,  was  found 
to  consist  largely  of  albite  feldspar  with  considerable  flaky  biotite. 
Calcite  is  fairly  common,  and  apatite,  titanite,  and  magnetite  occur 
as  accessory  minerals. 

AGE. 

The  Jualin  diorite  is  younger  than  the  Berners  formation,  which 
it  intrudes,  and  as  it  has  escaped  the  dynamic  deformation  to  which 
the  quartz  diorite  gneiss  was  subjected,  it  is  an  intrusive  mass  of 
later  age  than  that  of  the  great  body  of  granitoid  rocks  which  form 
the  backbone  of  the  Coast  Range  in  this  latitude.  No  evidence  is  at 
hand  to  fix  any  limit  to  the  length  of  time  elapsing  between  the  two 
periods  of  intrusion,  but  so  far  as  our  present  knowledge  of  south- 
eastern Alaska  geology  shows  the  interval  was  not  great. 

HORNBLENDITE. 

A small  area  of  a granular  basic  rock  strikingly  different  from  the 
Jualin  diorite  occurs  about  2 miles  north  of  the  mouth  of  Johnson 
Creek.  It  is  poorly  and  unsatisfactorily  exposed  on  account  of  the 
deep  growth  of  moss,  the  profusion  of  vegetation,  and  the  talus 
slopes  from  the  cliffs  of  Jualin  diorite,  and  its  relation  to  the  adjoin- 
ing rocks  was  not  determined.  It  may  be  either  a basic  phase  of 
the  Jualin  diorite  or  an  independent  intrusion. 


26 


THE  BERNERS  BAY  REGION,  ALASKA. 


The  hornblendite  is  a heavy  black  rock  composed  mainly  of  horn- 
blende. Abrupt  variations  in  texture  and  composition  are  of  gen- 
eral occurrence  and  give  the  rock  a wide  range  in  appearance.  The 
hornblende  in  places  forms  prisms  up  to  2 inches  in  length  and  is 
characterized  by  its  brilliant  cleavage  faces  and  metallic  luster  on 
cross-fractured  surfaces.  Locally  feldspar,  in  part  converted  to 
epidote,  occupies  the  triangular  interstices  between  the  hornblende 
prisms. 

THE  ORE  BODIES. 

INTRODUCTORY  STATEMENT. 

The  ore  bodies  of  the  Berners  Bay  region  are  gold  ore  deposits  of  low 
grade.  On  the  basis  of  form  they  may  be  classified  into  three  varie- 
ties— (1)  fissure  veins,  (2)  stockworks  or  irregular  masses  of  diorite 
ramified  by  quartz  veinlets,  and  (3)  stringer  lodes.  This  threefold 
division,  although  of  no  genetic  significance,  expresses  certain  well- 
marked  characteristics  of  the  ore  bodies  and  can  in  most  of  them  be 
maintained. 

The  largest  number  of  ore  deposits,  as  well  as  those  economically 
most  important,  lie  within  the  area  of  the  Jualin  diorite  and  are 
either  in  the  form  of  fissure  veins  or  stockworks.  The  stringer  lodes 
are  numerous  in  the  slates  and  graywackes  of  the  Berners  formation, 
but  have  not  yet  proved  to  be  of  commercial  value. 

The  outcrops  of  the  ore  bodies  lying  below  timber  line  are  much 
obscured  by  vegetation.  Some  are  completely  grown  over  with 
moss  and  have  trees  growing  on  the  very  tops  of  the  ledges;  they 
were  therefore  most  effectively  concealed  over  the  greater  part  of 
their  lengths  prior  to  discovery.  Above  timber  line  the  exposures, 
where  not  hidden  by  talus  slopes,  are  better.  The  longest  known 
outcrops  range  from  1,500  to  2,000  feet. 

The  deepest  continuous  development  work  has  attained  a depth  of 
600  feet  below  the  outcrop  of  the  ore  body,  and  one  stockwork  has 
been  intersected  at  850  feet,  although  the  continuity  of  the  deposit 
has  not  been  tested.  At  the  time  of  examination  the  length  of  any 
level  on  the  strike  of  any  ore  body  accessible  to  the  writer  did  not 
exceed  a few  hundred  feet. 

FISSURE  VEINS. 

The  fissure  veins,  with  few  exceptions,  are  restricted  in  their  occur- 
rence to  the  area  occupied  by  the  Jualin  diorite.  Most  of  the  ore 
bodies  belong  to  this  type  but  are  exceeded  in  size  by  the  stockwork 
deposits.  They  are  simple  quartz-filled  fractures  with  well-defined 
walls.  The  average  vein  has  a mean  thickness  of  5 feet;  the  maxi- 
mum width  of  solid  quartz  known  at  any  point  is  15  feet.  A marked 
tendency  to  swell  and  pinch  gradually  along  the  strike  and  dip  is 
exhibited  by  many  of  the  veins,  which  thereby  form,  as  it  were,  a 


THE  ORE  BODIES. 


27 


connected  series  of  long  flattened  lenses.  The  scanty  data  at  hand 
seem  to  show  that  the  average  length  of  the  longer  axes  of  these 
lenses  is  400  feet.  This  tendency  is  in  part  an  original  character- 

N 


Figure  2.— Diagram  showing  strike  of  veins. 


istic  due  to  the  mode  of  formation  of  the  veins,  and  is  in  part  due  to 
movements  along  postmineral  fractures  making  a narrow  angle  with 
the  plane  of  the  vein.  Where  the  variation  in  the  width  of  a vein 
is  due  to  such  displacements  the  swelling  or  pinching  is  usually 
more  abrupt  than  where  it  is  due  to  the  original  shape  of  the  Assure. 


The  strike  of  individual  veins  is  fairly  regular,  but  no  system  in 
the  strike  of  the  veins  as  a whole  can  be  observed.  The  greater 


28 


THE  BERNERS  BAY  REGION,  ALASKA. 


number,  however,  lie  in  the  nortli west-southeast  quadrants  (fig.  2). 
The  veins  dip,  almost  without  exception,  to  the  east  or  northeast  at 
angles  ranging  in  different  ledges  from  40°  to  70°  (ng.  3),  but  certain 
veins  show  as  great  a variation  as  this  from  level  to  level. 

STOCKWORKS. 

The  stockworks  are  masses  of  broken  country  rock  intricately 
penetrated  by  quartz  stringers.  The  representatives  of  this  type 
are  not  numerous  and  are  of  low  grade,  but  on  account  of  the  large 
tonnage  of  ore  which  they  seem  capable  of  furnishing  they  appear  to 
form  the  most  valuable  asset  of  the  region.  They  lie  in  the  area  of 
the  Jualin  diorite.  They  are  irregular  in  shape  and  are  not  bounded 
by  walls.  The  whole  mass  of  country  rock  and  included  network  of 
quartz  veins  constitutes  the  ore  body,  and  as  the  tenor  of  the  ore  is 
dependent  on  the  amount  of  included  quartz,  the  size  of  any  ore 
body  is  determined  partly  by  the  dictates  of  economic  expediency — 
that  is,  the  distinction  between  what  is  ore  and  what  is  not  ore  is 
determined  by  the  working  costs.  At  the  Kensington  mine,  on  a 
study  of  which  our  knowledge  concerning  these  deposits  chiefly  rests, 
the  ore  body  approximates  an  ellipse  in  cross  section  160  feet  long 
by  80  feet  wide.  The  quartz  veins  are  most  closely  spaced  near  the 
center  of  the  ore  body  but  toward  the  periphery  become  more  widely 
spaced,  so  that  the  large  amount  of  barren  diorite  included  in  the 
deposit  decreases  the  assay  value  of  the  ore  below  a profitable  limit. 

STRINGER  LODES. 

The  stringer  lodes  are  belts  of  schistose  country  rock  ribboned  with 
veinlets  of  quartz.  They  are  characteristically  developed  in  the 
graywackes  and  slates  of  the  Berners  formation  and  follow  the 
structure  of  the  inclosing  rocks.  An  enormous  number  of  quartz 
stringers  occur  in  the  sedimentary  rocks,  but  few  of  them  carry  any 
metallic  minerals,  so  that  comparatively  little  exploration  work  has 
been  attempted  on  them.  At  a few  localities  stringer  lodes  have 
been  partly  developed,  but  not  sufficiently  to  demonstrate  economic 
importance. 

At  other  points  in  the  Juneau  gold  belt  stringer  lodes  in  slate  have 
proved  to  be  of  great  value,  so  that  the  discovery  of  commercially 
valuable  lodes  of  this  character  in  the  Berners  Bay  region  is  not 
inherently  improbable.  The  general  law  of  the  occurrence  of  stringer 
lodes  in  the  Juneau  gold  belt  shows  that  they  are  most  likely  to  lie 
along  the  contact  of  a belt  of  slate  with  a harder  bed,  which  is  com- 
monly either  a sheet  of  greenstone  or  a stratum  of  graywacke. 


THE  OKE  BODIES. 


29 


MINERALOGY  OF  THE  ORE  DEPOSITS. 

Introductory  statement. — The  mineralogy  of  the  ore  deposits  is 
extremely  simple.  In  the  veins  the  minerals  constitute  the  material 
that  forms  the  filling  of  the  fissures;  in  the  stockworks  and  stringer 
lodes  they  include  the  minerals  of  the  country  rock  or  the  minerals 
derived  from  their  alteration  under  the  action  of  the  mineral-bearing 
solutions.  The  variety  is  not  great,  nor  are  the  minerals  distin- 
guished by  any  peculiarities  of  crystallization.  Oxidation  products 
are  not  common. 

Gold. — The  low-grade  ores  rarely  show  any  gold  visible  to  the  eye. 
It  is  reported,  however,  that  gold  was  found  intergrown  with  quartz 
in  masses  of  considerable  size  in  pockets  in  the  Comet  mine.  In  the 
upper  parts  of  some  lodes  it  appears  in  bright-yellow  particles  em- 
bedded in  iron  ocher,  where  it  has  evidently  been  derived  from  the 
oxidation  of  a pyritic  mineral.  At  the  Jualin  mine  it  is  closely 
associated  with  chalcopyrite,  commonly  intergrown,  and  is  with 
difficulty  distinguished  on  account  of  the  almost  identical  similarity 
of  color  between  gold  and  chalcopyrite.  Gold  occurs  also  embedded 
in  calcite. 

Copper. — Native  copper  was  not  observed  in  any  of  the  mines,  but 
is  reported  to  have  been  found  in  the  stream  bed  of  Johnson  Creek 
below  the  Jualin  mine.  The  presence  of  chalcopyrite  and  some  of 
its  oxidation  products,  azurite  and  malachite,  in  that  lode  leaves 
little  doubt  that  the  native  metal  was  derived,  like  the  carbonates, 
from  the  oxidation  of  copper  pyrites. 

Galena. — The  lead-gray  sulphide  of  lead  occurs  in  small  particles 
embedded  in  the  quartz  of  the  veins  and  stringers.  It  occurs  no- 
where in  the  altered  wall  rock,  differing  notably  in  this  respect  from 
pyrite.  It  shows  no  crystallographic  boundaries,  but  exhibits  the 
characteristic  cubical  cleavage. 

Sphalerite. — Sphalerite  was  noted  at  only  two  of  the  properties  in 
the  district — the  Jualin  and  the  Fremming.  At  the  Fremming  it  is 
of  yellowish-brown  color  and  occurs  together  with  galena,  pyrite, 
chalcopyrite,  and  free  gold.  Minute  amounts  of  black  sphalerite 
occur  at  the  Jualin  mine. 

Chalcopyrite. — Chalcopyrite,  the  gold-yellow  sulphide  of  copper 
and  iron,  is,  next  to  pyrite,  the  commonest  metallic  sulphide  in  the 
region.  Its  presence  seems  favorable  to  good  values  in  gold,  and 
gold  is  often  found  inclosed  in  it  at  the  Jualin  mine.  As  a rule,  the 
chalcopyrite  occurs  embedded  in  quartz  in  irregular  particles  with- 
out crystal  faces,  but  where  it  lines  drusy  cavities  it  forms  small 
tetrahedrons.  Chalcopyrite  may  be  distinguished  from  pyrite,  with 
which  it  may  sometimes  be  confused,  by  its  comparative  softness, 
for  it  scratches  readily,  and  its  deeper  yellow  color. 


30 


THE  BERNERS  BAY  REGION,  ALASKA. 


Pyrite. — The  pale  brass-yellow  sulphide  of  iron,  pyrite,  is  the 
most  abundant  metallic  mineral  in  the  region.  Unlike  the  other 
sulphides — galena,  sphalerite,  and  chalcopyrite — it  occurs  both  in 
the  vein  fillings  and  in  the  altered  wall  rocks.  The  pyrite  is  both 
massive  and  crystalline;  where  crystallized  it  is  commonly  in  the 
form  of  striated  cubes  and  rarely,  as  at  the  Indiana  property,  in  fine 
octahedrons. 

Quartz. — The  principal  nonmetalliferous  mineral  forming  the  vein- 
filling material  of  the  region  is  a white  quartz  of  fairly  coarse  texture. 
Some  of  the  veins  are  characterized  by  a drusy  structure,  and  in 
these  the  quartz  is  partly  bounded  by  crystal  faces,  and  terminated 
prisms  project  into  the  vugs.  The  central  portion  of  the  Ophir  vein 
contains  cavities  several  feet  long,  and  these  are  implanted  with 
large  glassy  crystals  of  quartz. 

Calcite. — Calcite  occurs  as  a subordinate  constituent  in  all  the 
quartz  veins  but  as  a rule  is  prominent  only  in  the  stringers.  Sparry 
masses  occur  in  places  in  the  altered  diorite  wall  rock;  some  is  of 
reddish-brown  color,  but  as  it  is  easily  soluble  in  cold  hydrochloric 
acid,  it  is  probably  a ferriferous  calcite  and  not  siderite,  as  was  sus- 
pected. 

Dolomite. — The  presence  of  dolomite  is  indicated  by  the  micro- 
scope as  an  alteration  product  of  the  diorite  adjoining  quartz  veins. 
It  is  recognized  in  the  larger  aggregates  by  its  strongly  curved  cleav- 
age and  by  its  tentlency  to  form  perfect  rhombohedrons  scattered 
throughout  the  altered  diorite.  It  was  positively  identified  by  de- 
termining the  value  of  the  refractive  index  co. 

Feldspar. — The  feldspar  of  the  Jualin  diorite  is  an  important  con- 
stituent of  the  stockwork  ore  bodies,  such  as  the  Eureka,  the  Ken- 
sington, and  the  Johnson.  It  is  a plagioclase  (commonly  ande- 
sine)  or  labradorite,  but  instead  of  showing  the  white,  pearly  ap- 
pearance of  ordinary  feldspar,  it  is  light  greenish  and  possesses 
rather  an  oily  luster  due  to  a more  or  less  thorough  alteration  to 
sericite.  A clear  glassy  feldspar,  which  the  microscope  shows  to  be 
albite,  is  in  places  associated  with  the  altered  plagioclase  feldspar, 
from  whose  transformation  it  has  been  derived  by  the  action  of 
vein-forming  solutions.  It  is  also  found  in  microscopic  veinlets  in 
the  altered  diorite  along  with  quartz  and  calcite  or  dolomite.  Its 
presence  throws  important  light  on  the  character  of  these  solutions 
and  allies  the  mineralization  with  that  wliich  has  taken  place  at  the 
Treadwell  deposits.  Albite  has  not  been  noted  as  a macroscopic 
component  of  the  larger  quartz  veins,  but  its  discovery  seems  not 
unlikely. 

Sericite. — Scales  of  silvery-wliite  mica  occur  in  the  vem  quartz, 
but  nowhere  in  large  amount.  It  is,  as  already  indicated,  abundant 
as  a microscopic  constitutent  of  the  altered  feldspar  of  the  diorite 
wall  rock. 


THE  ORE  BODIES. 


31 


Hornblende. — Hornblende  in  its  unaltered  condition  is  a dark- 
green  or  black  prismatic  mineral,  which  is  a prominent  constituent 
of  the  Jualin  diorite.  Under  the  action  of  mineralizing  solutions  it 
has  been  converted  into  epidote  and  chlorite. 

Epidote. — Epidote,  a hydrous  aluminum  silicate  of  calcium  and 
iron,  is  a mineral  of  bright  yellowish-green  color.  It  is  present  in 
the  hydrothermally  altered  diorite  in  a finely  disseminated  condi- 
tion, and  is  responsible  in  considerable  measure  for  the  greenish  hue 
that  the  diorite  assumes  in  the  vicinity  of  the  ore  bodies. 

Chlorite. — Chlorite  is  a micaceous  or  foliated  mineral  of  deep-green 
color.  It  is  abundant  in  the  stockwork  deposits  as  an  alteration 
product  of  biotite,  which  is  one  of  the  pyrogenetic  constituents  of 
the  Jualin  diorite.  It  is  in  part  derived  also  from  hornblende.  The 
pyrite  in  the  country  rock  is  commonly  associated  with  chlorite, 
much  of  which  shows  sagenitic  webs.  The  fibers  or  prisms  making 
up  these  webs  are  in  some  places  sufficiently  coarse  to  show  the 
diagnostic  properties  of  rutile,  such  as  deep  pleochroism,  straight 
extinction,  and  relief. 


VALUE  OF  THE  ORES. 

The  ores,  if  $10  a ton  is  considered  to  fix  the  upper  limit  in  value 
of  low-grade  ores,  are  commonly  of  low  grade.  The  Comet  mine, 
one  of  the  two  largest  producers  in  the  region,  averaged  $9.20  a ton 
for  a production  of  50,000  tons.  On  the  other  hand,  a number  of 
strong  fissure  veins  averaging  5 feet  in  thiclmess,  from  which  a con- 
siderable tonnage  of  ore  has  been  mined  and  milled,  have  yielded 
only  $3  to  the  ton— an  amount  that  under  present  conditions  is  below 
the  working  costs. 

The  highest  grade  ore  in  the  region  was  extracted  from  one  of 
the  veins  of  the  Jualin  mine  and  averaged  $30  a ton  over  a width  of 
7 feet.  It  is  a noteworthy  fact  that  the  ore  of  this  mine  is  compara- 
tively high  in  metallic  sulphides. 

Few  data  are  available  concerning  the  value  of  the  ore  of  the  stock- 
work  deposits.  The  general  rule  seems  to  hold  that  the  values  in- 
crease proportionately  to  the  size  and  number  of  quartz  stringers  per 
volume  of  country  rock.  The  Eureka  is  said  to  average  $7  a ton 
over  a width  of  18  feet,  the  Kensington  from  $3  to  ^$5  over  a width 
of  80  feet. 

FISSURE  AND  VEIN  FORMING  PROCESSES. 

The  formation  of  the  veins  required  the  intervention  of  two  sepa- 
rate processes — the  fracturing  and  opening  of  the  fissures  and  the 
filling  of  the  fissures  with  quartz  and  the  metalliferous  constituents. 
The  second  process  tends  to  obscure  and  obliterate  certain  of  the 
records  of  the  first. 


32 


THE  BERNERS  BAY  REGION,  ALASKA. 


Some  of  the  veins  are  in  places  adjoined  by  belts  of  mashed  diorite 
which  have  the  structure  of  a closely  foliated  green  schist.  Frag- 
ments of  this  schist  inclosed  in  the  veins  prove  that  the  crushing  of 
the  diorite  took  place  prior  to  the  introduction  of  the  vein-filling 
material,  but  it  is  improbable  that  this  green  schist  with  its  present 
mineral  make-up  is  the  product  of  the  mechanical  alteration  of  the 
diorite.  It  has  been  too  thoroughly  affected  by  the  ore-depositing 
agencies  to  retain  its  original  composition.  Viewed  under  the  micro- 
scope, the  schist  proves  to  be  composed  largely  of  altered  plagioclase 
and  sericite,  with  a minor  amount  of  calcite  and  accessory  chlorite, 
magnetite,  and  apatite.  The  green  color  of  the  schist  is  due  to  the 
presence  of  the  sericite. 

Narrow  portions  of  some  of  the  veins  are  occupied  by  schistose 
diorite  or  are  filled  with  broken  masses  of  diorite  interlaced  with 
quartz  stringers.  All  these  features  indicate  that  powerful  compres- 
sive forces  were  operative  in  producing  the  fractures. 

At  other  points  in  the  region  these  stresses  have  produced  belts  of 
schist  in  the  diorite,  but  these  schistose  zones  have  remained  unmin- 
eralized, possibly  because  they  were  too  tight  to  furnish  free  circula- 
tion to  the  ore-depositing  agencies.  One  of  the  schists — a light-green 
foliated  rock  from  a zone  10  feet  thick  in  the  Indiana  tunnel — was 
found  to  consist  of  highly  altered  plagioclase  which  is  much  obscured 
by  sericite  and  carbonate.  The  sericite  shows  no  schistose  arrange- 
ment like  that,  for  example,  characterizing  deformed  quartz  por- 
phyries; the  carbonate  is  commonly  scattered  throughout  the  feldspars 
in  the  form  of  small  rhombohedrons.  Both  minerals  are  character- 
istic of  the  chemically  altered  wall  rock  that  adjoins  the  ore  bodies. 
A number  of  small  radiate  groups  of  bluish-brown  tourmaline  occur 
throughout  the  rock,  and  pyrite,  magnetite,  and  apatite  are  present 
as  accessory  minerals.  The  tourmaline  was  introduced  subsequent 
to  the  shearing  of  the  rock,  and  tourmalinization  appears  to  have 
been  contemporaneous  with  the  sericitization  and  carbonatization. 

In  addition  to  the  mechanical  alteration  of  the  wall  rocks,  they 
have  been  affected  by  a chemical  alteration  due  to  the  activity  of 
the  agencies  that  brought  in  the  quartz  and  metallic  minerals.  The 
width  of  wall  rock  affected  by  this  alteration  varies,  ranging  up  to 
several  feet.  The  alteration  is  most  intense  where  the  wall  rock  is 
irregularly  penetrated  by  stringers  branching  from  the  main  lode. 

The  general  course  of  the  alteration  of  the  diorite  leads  to  the 
chloritization  and  destruction  of  the  ferromagnesian  minerals,  to  the 
partial  sericitization  of  the  plagioclase  feldspar,  to  the  formation  of 
albite,  and  to  the  introduction  of  carbonates  (dolomitic  in  part)  and 
pyrite.  In  short,  the  diorite  is  transformed  mainly  by  recrystalli- 
zation, durmg  which  there  is  some  addition  of  carbon  dioxide  and 


THE  ORE  BODIES. 


33 


sulphur  and  probably  of  iron  and  potash.  The  process  is  very  similar 
uO  that  determined  for  tlie  Treadwell  ore  deposit  by  Spencer,®  who 
pointed  out  that,  though  the  occurrence  of  albite  is  fairly  common  in 
certain  types  of  gold-quartz  veins,  it  had  not  previously  been  detected 
in  the  metasomatically  altered  wall  rocks  of  any  veins  that  had  been 
studied.  It  has  been  noted  by  Lindgren^  to  form  in  albite-rich 
amphibolites. 

The  most  tliorough  alteration  observed  in  the  Berners  Bay  region 
was  that  adjoining  portions  of  the  Bear  vein.  Here  the  diorite  has 
been  converted  into  a nearly  snow-white  rock  impregnated  with  small 
cubes  of  pyrite.  In  thin  section  this  rock  is  seen  to  have  a crushed 
granulated  structure  healed  b}^  recrystallization  and  obscured  by 
metasomatic  alteration.  Plagioclase  is  the  main  constituent  and  is 
largely  altered.  It  is  sericitized,  especially  where  pyrite  has  been 
introduced,  and  in  places  contains  rhombohedrons  of  carbonate. 
Patches  of  recrystallized  clear  glassy  feldspar,  which  proves  to  be 
albite,  occur  sporadically.  Replaced  areas  consisting  of  carbonate 
that  shows  strongly  curved  cleavage,  quartz,  and  subordinate  albite 
are  present.  The  carbonate  was  proved  to  be  dolomite  by  determin- 
ing the  value  of  (j)  according  to  Schroeder  van  der  Kolk’s  method;® 
this  value  was  found  to  be  1.69. 

It  is  not  possible  to  obtain  the  fresh  diorite  from  which  this  wall 
rock  was  derived.  At  550  feet  from  the  vein  the  diorite  shows 
numerous  hornblende  prisms  resting  in  dull-green  aphanitic  matrix. 
In  thin  section  this  apparent  matrix  is  found  to  consist  of  highly 
altered  feldspar  and  primary  interstitial  quartz.  The  feldspar,  mainly 
plagioclase  with  some  orthoclase,  is  thoroughly  sericitized.  Epido'te, 
chlorite,  and  carbonate  are  common;  pyrite  occurs  s[)oradically. 
The  presence  of  magnetite  as  a relatively  abundant  accessory  mineral 
is  noteworthy.  The  hornblende  which  is  so  readily  seen  in  the  hand 
specimens  proves  to  be  considerably  altered;  the  presence  of  chlorit- 
ized  biotite  is  suggested  but  can  not  be  established. 

Where  the  metasomatic  alteration  has  been  less  intense,  as  in  the 
diorite  of  the  Kensington  stockwork  or  at  the  Jualin  mine,  the  altered 
wall  rock  consists  essentially  of  an  aggregate  of  sericitized  plagioclase 
and  chloritized  biotite  which  shows  sagenitic  webs.  No  recognizable 
vestiges  of  hornblende  are  present.  In  places  considerable  apatite 
occurs  as  an  accessory  mineral.  The  veinlets  of  quartz  that  traverse 
this  altered  rock  contain  dolomite  and  calcite,  a little  sericite  and 
chlorite,  and  some  glassy  striated  subhedral  albite.  In  places  the 

a Bull.  U.  S.  Geol.  Survey  No.  287,  1906,  p.  113. 

^ Lindgren,  Waldemar,  Econ.  Geology,  vol.  2,  1907,  p.  11 
c Determined  by  E.  S.  Larsen. 

67811°— Bull.  446—11 3 


34 


THE  BERNERS  BAY  REGION,  ALASKAo 


limpid  new  albite  adjoins  highly  sericitized  feldspar,  and  the  contrast 
between  original  and  secondary  feldsoar  is  strikingly  apparent. 
Some  of  the  smaller  veinlets  are  composed  entirely  of  dolomite  and 
albite. 

At  a greater  distance  from  the  ore  bodies,  hornblencle  begins  to 
appear  in  the  diorite.  It  is  partly  epidotized  and  chloritized;  epidote 
appears  also  in  the  plagioclase,  together  with  carbonate  and  sericite. 
The  biotite  is  partly  chloritized,  commonly  around  the  edges,  and 
contains  finely  developed  sagenitic  webs,  especially  in  the  chloritized 
])ortions.  Zoisite  is  noted  here  and  there.  Magnetite  appears  among 
the  ordinary  accessory  minerals  of  the  diorite. 

The  mineralogical  study  of  the  metamorphism  of  the  diorite  wall 
rocks  shows  that  where  the  alteration  was  most  profound  the  femic 
minerals,  especially  the  hornblende  and  magnetite,  were  destroyed 
and  all  traces  of  their  former  presence  completely  obliterated.  The 
iron  of  tliese  minerals  was  used  to  form  pyrite;  the  lime  and  magnesia 
of  the  hornblende  to  form  dolomite.  The  feldspar  has  been  partly 
sericitized  and  recrystallized  to  albite.  The  potash  of  the  sericite 
was,  in  part  at  least,  furnished  by  the  biotite.  Apatite  remains 
throughout  the  course  of  alteration.  Epidote  is  not  formed  in  the 
zone  of  most  intense  metasomatism,  but  appears  in  the  zone  of  feebler 
alteration. 

The  alteration  of  the  wall  rock  has  been  mainly  in  the  nature  of  a 
chemical  rearrangement  of  the  constituent  molecules,  modified  to 
some  extent  by  the  introduction  of  sulphur  and  carbon  dioxide  and 
by  the  })artial  elimination  of  soda.  In  general,  the  amount  of  pyrite 
developed  in  the  wall  rock  seems  to  have  been  determined  by  the 
amount  of  iron  originally  present  in  the  ferromagnesian  minerals  and 
magnetite. 

The  chemical  work  done  by  the  ore-depositing  agencies  shows  that 
they  were  hot  ascending  solutions  carrying  carbon  dioxide,  sulphur 
(probably  as  hydrogen  sulphide),  silica,  potash,  gold,  iron,  and  several 
heavy  metals  in  small  quantities,  and  doubtless  other  constituents 
that  have  left  no  record  of  their  presence  because  they  remained 
unfixed  either  in  the  vein  stuff  or  in  the  altered  wall  rocks.  At  one 
locality  the  solutions  were  capable  of  causing  the  formation  of 
tourmaline  as  well  as  producing  sericitization  and  carbonatization. 
The  occurrence  of  this  tourmaline  tends  to  corroborate  the  conclusion 
previously  reached  concerning  the  comparatively  highly  heated 
character  of  the  vein-forming  solutions.  Too  weighty  a superstruc- 
ture of  argument  should  not  be  built  on  this  single  occurrence,  but  it 
suggests  that  when  the  mining  development  of  the  region  is  further 
advanced  and  increased  facilities  for  investigation  are  provided  the 
relation  of  the  tourmalinization  and  auriferous  mineralization  can. 
be  more  firmly  established. 


THE  OKE  BODIES. 


35 


ORIGIN  OF  THE  ORE  DEPOSITS. 

The  problem  concerning  the  origin  of  the  ore  deposits  involves  the 
consideration  of  two  factors — the  origin  of  the  fractures  and  the 
origin  or  source  of  the  vein  stuff  and  its  metalliferous  constituents. 

( impressive  forces,  as  indicated  by  the  schistose  nature  of  the  wall 
rocks,  caused  the  initial  fracturing  of  the  rocks.  The  surfaces  along 
which  this  rupturing  took  place  were  not  simple  planes,  but  were 
ratlier  of  gently  undulating  character  along  both  the  strike  and  the 
dii  ),  as  shown  by  the  stoped-out  portions  of  the  veins,  and  subsequent 
movements  along  the  fractures  produced  the  open  spaces  in  which 
the  quartz  and  metallic  minerals  were  later  deposited. 

The  fissures  show  neither  conjugate  relations  nor  any  other  dis- 
cernible systematic  arrangement.  In  a highly  speculative  paper 
Spencer  ® has  put  forth  a conception  of  the  origin  of  the  fissures  in  the 
Juneau  gold  belt,  but  inasmuch  as  the  conditions  ])‘ostulated  in  his 
argument  do  not  exist  in  the  Berners  Bay  country  his  ideas  can  not 
be  applied  to  that  region. 

The  localization  of  the  largest  number  of  ore  bodies  in  the  area  of 
the  Jualin  diorite  is  the  most  striking  fact  in  the  geology  of  the  region. 
It  suggests  a genetic  dependence  on  that  rock  mass,  but  what  that 
genetic  relation  is  can  not  easily  be  established. 

The  mineralogical  character  of  the  veins  throws  no  light  on  the 
origin  of  the  deposits.  The  metallic  minerals — gold,  pyrite,  chal- 
copyrite,  galena,  and  sphalerite — and  the  gangue  mineral  quartz  all 
belong  to  the  grouj)  of  persistent  minerals,^  and  are  therefore  of 
little  genetic  significance. 

The  character  of  the  metasomatic  alteration  of  the  wall  rock  affords 
a more  hopeful  line  of  attack  on  the  problem.  The  study  of  that 
process  has  shown  tliat  the  vein-forming  solutions  were  capable  of 
» effecting  an  intense  hydrothermal  metamorphism,  a characteristic 
feature  of  which  is  the  development  of  albite  in  the  altered  rock 
as  well  as  in  the  narrow  veinlets  penetrating  the  altered  wall  rock. 
This  feature,  as  already  pointed  out,  allies  the  character  of  the  min- 
eralization to  that  which  has  produced  the  Treadwell  lode,  so  that 
this  similarity  is  one  of  both  practical  and  theoretical  significance. 
The  presence  of  albite  appears  to  be  a regional  characteristic  of  the 
Juneau  gold  belt,  and,  on  account  of  the  known  instability  of  soda 
minerals  in  veins  formed  at  moderate  or  shallow  depths, indicates 
a deep-seated  origin  for  the  gold  veins. 

The  hypothesis  of  a magmatic  origin  for  the  vein-forming  waters 
in  southeastern  Alaska  was  first  advanced  by  Spencer‘s  and  was 

a Spencer,  A.  C.,  The  origin  of  vein-filled  openings  in  southeastern  Alaska:  Trans.  Am.  Inst.  Min.  Eng., 
vol.  36,  1906,  pp.  1211-1216. 

b Ivindgren,  Waldemar,  The  relation  of  ore  deposition  to  physical  condition:  Econ.  Geology,  vol.  2, 1907, 

p.  122. 

c Lindgren,  Waldemar,  op.  cit.,  p.  117. 

d Spencer,  A.  C.,  Trans.  Am.  Inst.  Min.  Eng.,  vol.  36, 1906,  p.  971;  also  Bull.  U.  S.  Geol.  Survey  No.  287, 
1906,  p.  30, 


36 


THE  BEENERS  BAY  REGION,  ALASKA. 


based  mainly  on  the  facts  observed  in  the  Juneau  district.  These 
included  the  relation  of  mineralization  to  intrusive  rocks,  the  nature 
of  the  metasomatic  processes,  and  the  sporadic  presence  of  pneu- 
niatolytic  minerals  in  the  veins. 

All  subsequent  work  has  tended  to  support  this  hypothesis.  The 
geologic  map®  published  on  the  completion  of  reconnaissance  work 
in  southeastern  Alaska  shows  most  strikingly  the  clustering  of 
mineral  deposits  along  the  intrusive  contacts  of  granitoid  rocks. 
The  force  of  this  suggestive  relation  gains  cumulative  strength  when 
it  is  found  that  a similar  association  exists  along  the  eastern  margin 
of  the  diorite  core  of  the  Coast  Range. 

It  is  therefore  probable  that  in  a regional  treatment  of  the  ore 
deposits  of  southeastern  Alaska  the  hypothesis  of  Spencer  embod- 
ies an  important  generalization,  the  plausibility  of  which  may  not 
always  be  readily  apparent  when  applied  to  individual  deposits  or 
localities.  At  Berners  Bay  the  massing  of  the  ore  bodies  in  the  area 
of  the  Jualin  diorite  is  so  striking  a feature  that  a certain  mental 
restraint  is  required  to  keep  from  precipitately  embracing  the  mag- 
matic hypothesis. 

The  independent  evidence  that  the  region  as  an  isolated  unit  offers 
to  the  magmatic  hypothesis  consists,  first,  in  the  spatial  relation  of 
the  ore  bodies  to  the  diorite,  and,  second,  in  the  character  of  the 
metasomatic  alteration  of  the  wall  rocks.  From  the  present  status 
of  knowledge  concerning  the  origin  of  ore  bodies  it  may  be  regarded 
as  established  that  the  vein-forming  agencies  were  ascending  thermal 
solutions.  That  they  were  released  from  a cooling  magma  is  strongly 
suggested  but  not  proved.  The  tourmalinization  effected  by  solu- 
tions essentially  similar  in  composition  to  those  that  produced 
economic  mineralization  is  a fact  lending  support  to  the  magmatic 
hypothesis,  but  in  view  of  the  meager  distribution  of  the  tourmaline, 
so  far  as  known,  it  is  one  on  which  much  weight  can  not  be  laid. 

PRACTICAL  DEDUCTIONS. 

Any  enriched  surface  ores  that  may  have  existed  within  this  region 
have  been  swept  away  by  the  powerful  glacial  erosion  to  which  the 
region  was  subjected  in  the  recent  geologic  past.  The  ores  exposed 
at  the  surface  are  therefore  of  primary  origin,  modified  to  an  unim- 
portant extent  by  postglacial  oxidation,  and  the  outcrop  of  any  ore 
deposit  will  furnish  a true  index  of  the  value  of  the  lode  as  a whole, 
depending  on  whether  the  distribution  of  values  in  the  ore  is  or  is 
not  uniform.  As  some  of  the  veins  have  been  found  to  be  pockety 
and  as  many  an  undeveloped  prospect  is  known  from  a single  out- 
crop only  on  account  of  the  generally  poor  exposures  in  the  region,  it 


a Wright,  C.  W.,  Bull.  U.  S.  Geol.  Survey  No.  345, 1908,  Pi.  II. 


THE  ORE  BODIES. 


37 


may  happen  that  a surface  ore  may  give  results  that  are  either  liiglier 
or  lower  than  the  average  value  of  the  whole  ore  body. 

The  continuity  of  the  ore  deposits  in  depth  is  a matter  of  the 
highest  practical  interest.  It  is  dependent  on  two  factors — the  per- 
sistence of  the  Assuring  and  the  character  or  quality  of  the  mineraliza- 
tion. As  shown  by  the  microscopic  study  of  the  vein-forming 
processes,  the  quality  of  the  mineralization  is  such  as  to  assure  its 
maintenance  to  a depth  which  is  below  the  limit  of  profitable  mining. 
This  conclusion  is  enforced  by  both  theoretical  and  practical  con- 
siderations. The  Kensington  lode  outcrops  at  an  altitude  of  2,800 
feet;  the  Treadwell,  which  outcrops  near  sea  level,  has  been  proved 
to  a depth  of  1,700  feet  without  diminution  of  its  values.  This  gives 
a known  vertical  range  of  practically  4,500  feet  through  which  the 
auriferous  solutions  were  capable  of  precipitating  gold  in  the  Juneau 
district.  The  probabilities  are  that  this  is  a minimum  estimate,  but 
it  is  perhaps  well  to  point  out  that  this  figure  is  based  on  the  assump- 
tion that  the  ore  deposits  have  not  been  displaced  vertically  with 
reference  to  each  other  since  they  were  formed,  either  by  faulting 
or  by  crustal  warping. 

It  does  not  follow,  however,  that  the  quantity  of  mineralization 
persists  downward.  This  is  a function  of  the  extent  of  the  Assuring 
in  depth  and  the  persistence  of  size  of  the  veins  or  the  amount  of 
veination  in  the  stockworks.  These  factors  can  be  determined  much 
less  satisfactorily  than  those  relating  to  the  quality  of  mineralization. 

It  has  been  pointed  out  in  previous  pages  that  the  veins  were 
formed  by  the  movement  of  the  walls  past  each  other  along  gently 
sinuous  fractures.  Pinches  and  swells  are  therefore  encountered  on 
the  levels  along  the  strike  of  the  veins.  Similar  variation  is  to  be 
expected  vertically  also,  although  development  has  not  yet  been 
sufAciently  extensive  to  demonstrate  this  as  a law. 

Inasmuch  as  narrow  ])ortions  of  the  Assures  are  commonly  occupied 
by  masses  of  schistose  diorite  which  are  here  and  there  interlaced 
with  quartz  stringers,  such  schistose  zoiies  are  worth  exploring  or 
drifting  on  in  the  chance  of  striking  other  valuable  ore  bodies.  This 
possibility  was  forcibly  illustrated  at  the  Jualin  mine,  where  an  18- 
inch  zone  of  crushed  diorite  of  most  unpromising  appearance  opened 
out  when  followed  along  the  strike  into  a strong  and  valuable  ore 
body.  That  this  is  no  infallible  rule,  however,  is  clearly  demon- 
strated by  certain  fruitless  attempts  that  have  been  made  under  its 
guidance.  In  the  most  conspicuous  example  500  feet  of  tunnel  was 
drifted  along  a schistose  zone  in  the  diorite  without  encountering  a 
ledge.  The  probability  of  striking  an  ore  body  is  apparently  strongest 
in  those  belts  of  crushed  or  sheared  diorite  that  are  penetrated  by 
quartz  stringers. 


38 


THE  BERNERS  BAY  REGION,  ALASKA. 

(3n  the  whole,  the  downward  persistence  of  fissiiring  would  seem  to 
be  proved  by  the  deep-seated  origin  of  the  vein-forming  solutions, 
as  shown  by  the  alterations  that  they  were  able  to  effect  in  the  wall 
rocks.  The  ore  bodies  will  doubtless  show  variations  in  size  alonp’ 

o 

the  dip  and  strike,  but  the  character  of  the  diorite  country  rock  is 
favorable  to  their  continuity  in  depth. 

The  conclusion  that  the  ore  deposits  are  of  deep-seated  origin  and 
due  to  the  ascent  of  thermal  waters  is  ultimately  based  on  empirical 
generalizations  and  is  independent  of  any  speculative  conceptions  as 
to  the  magmatic  origin  of  those  solutions.  It  therefore  rests  uy)on  a 
firmer  foundation  and  lends  assurance  to  the  belief  that  the  ore 
deposits  will,  as  a rule,  persist  downward  below  the  limits  of  profitable 
extraction  without  essential  change  of  values. 

DESCRIPTIONS  OF  INDIVIDUAL  MINES  AND  PROS- 

PECTS.a 

The  mines  and  pros])ects  are  described  in  geographic  order,  those 
in  the  Sherman  Creek  drainage  basin  being  taken  up  first  and  those 
on  the  Berners  Bay  side  being  considered  last.  A large  number  of 
partly  developed  prospects  or  locations  are  not  described,  in  order  to 
avoid  a monotonous  repetition  of  uninstructive  details. 

IVANHOE  MINE. 

The  main  tunnel  of  the  Ivanhoe  mine  is  situated  miles  north- 
east of  Comet,  at  2,350  feet  above  sea  level.  This,  the  upper  working, 
was  connected  with  the  stamp  mill,  which  is  situated  on  Sherman 
Creek  at  an  altitude  of  500  feet,  by  a tramway  system  consisting  of 
3,000  feet  of  cable  tram  and  2,700  feet  of  gravity  tram.  This  system 
has  been  largely  destroyed  by  rock  and  snow  slides.  The  mill  is 
equipped  with  20  stamps  and  8 Frue  vanners  and  houses  the  com- 
pressor plant. 

The  principal  tunnel  bears  east  for  185  feet  to  a point  where  it 
intersects  the  vein  at  a depth  of  45  feet  below  the  outcrop;  a drift 
opens  the  vein  over  a length  of  850  feet.  At  one  point  ore  has  been 
stoped  out  to  the  surface,  and  3,000  tons  was  extracted,  reported 
to  have  yielded  about  $7,000.  The  property  has  been  idle  since  1903. 

The  vein  averages  5 feet  in  thickness,  ranging  from  1 to  9 feet,  and 
is  inclosed  between  well-defined  walls.  The  strike  is  N.  10°  W.  and 
the  dip  ranges  from  30°  to  60°  E.,  averaging  50°.  The  country  rock 
in  the  vicinity  of  the  Ivanhoe  mine  consists  of  altered  basalts  or 
diabase  porphyries.  These  are  dark-colored  fine  granular  rocks 
spotted  with  conspicuous  blebs  of  yellowish-green  epidote.  The 
original  bedded  character  of  the  rocks  is  obscure,  but  differences  of 

a The  writer  has  made  free  use  of  the  unpublished  notes  of  C.  W.  Wright  for  economic  data  and  for  infor- 
mation concerning  the  underground  development  of  mines  that  were  inaccessible  in  1909. 


DESCRIPTIONS  OF  MINES  AND  PROSPECTS. 


39 


texture  can  be  noted  from  place  to  place.  The  rock  50  feet  west  of 
the  tunnel  entrance  is  more  porphyritic  than  the  prevailing  variety. 
Tabular  feldspars  one-half  inch  long  form  the  phenocrysts  and  are 
arranged  here  and  there  in  stellate  groups. 

HORRIBLE  MINE. 

The  Horrible  group  of  five  claims  was  located  in  1896  and  was 
sold  late  in  the  same  year  to  the  Portland- Alaska  Mining  Company. 
Mining  operations  were  begun  in  the  spring  of  1897,  and  an  aerial 
tramway  2 miles  long  was  erected  which  connected  the  mine  workings 
with  a 10-stamp  mill  built  on  the  shore  of  Lynn  Canal.  Work  was 
suspended  during  the  winter  of  that  year  and  was  resumed  only  for 
a short  time  in  1901. 

The  mine  is  opened  by  a tunnel  400  feet  long  drifted  on  the  ledge, 
which  strikes  north  and  south  and  dips  steeply  to  the  east.  The  ore 
body  consists  of  a quartz-filled  fissure  whose  walls  are  commonly 
well  defined  and  which  ranges  in  width  from  a seam  to  10  feet,  averag- 
ing 5 feet.  The  quartz  is  sparingly  mineralized  with  metallic  min- 
erals; the  only  one  visible  to  the  eye  is  pyrite.  The  country  rock 
inclosing  the  vein  is  a green  diorite  of  rather  fine  texture.  The 
hanging-wall  side  has  been  explored  by  a drift  240  feet  long,  but  no 
ore  body  was  encountered. 

Some  stoping  was  done  on  the  vein  and  500  tons  of  ore  was  ex- 
tracted; this  is  reported  to  have  yielded  $1,500  in  gold. 

OPHIR  GROUP. 

The  Ophir  vein  outcrops  prominently  at  an  altitude  of  1,500  feet 
along  the  fiank  of  the  mountain  north  of  Sherman  Creek.  Three 
tunnels  have  been  driven  on  the  property,  two  of  which  cut  the  vein. 
The  third,  which  is  300  feet  long,  is  planned  to  undercut  the  ore  body 
at  a depth  of  200  feet,  but  has  not  been  completed.  The  two  upper 
tunnels  are  400  feet  apart  on  the  strike  of  the  vein,  and  drifts  aggre- 
gating 300  feet  have  been  driven  along  its  course. 

The  country  rock  at  the  Ophir  vein  is  a greenish  diorite  characterized 
by  an  abundance  of  small  black  prisms  of  hornblende.  The  ore  body 
is  a simple  quartz-filled  fissure  vein  striking  N.  30°  W.  and  dipping 
on  an  average  45°  E.  It  ranges  in  thickness  from  2 to  6 feet.  The 
quartz  is  practically  devoid  of  pyritic  mineralization,  sporadic  par- 
ticles of  iron  pyrite  only  being  present.  The  Ophir  vein  is  rendered 
notably  different  from  others  in  the  district  through  the  presence  of 
numerous  vugs  and  cavities  lined  with  large  glassy  quartz  crystals. 

BEAR  MINE. 

The  Bear  mine  is  situated  on  the  north  slope  of  Sherman  Creek  at 
an  elevation  of  1,350  feet  and  is  connected  with  the  40-stamp  mill  of 
the  Berners  Bay  Mining  and  Milling  Company  by  a gravity  tramway 


40 


THE  BERNERS  BAY  REGION,  ALASKA. 


1,700  feet  long.  The  mine  is  developed  by  an  adit  level  1,100  feet 
long,  which  crosscuts  the  Bear  vein  500  feet  from  the  portal  and 
200  feet  below  the  outcrop.  The  additional  600  feet  is  said  to  have 
been  driven  in  pursuance  of  a plan  to  eventually  undercut 'the 
Kensington  lode  at  this  greatly  increased  depth.  A raise  was  put 
through  to  the  surface  on  the  Bear  vein  and  three  levels  from  250  to 
300  feet  long  have  been  worked.  From  these  considerable  ore  has 
been  stoped  in  places,  the  stopes  reaching  the  surface.  During  the 
years  1895  to  1897  about  5,500  tons  was  extracted. 

The  country  rock  at  the  Bear  mine  is  a greenish  diorite  whose 
green  color  in  due  mainly  to  the  presence  of  finely  disseminated 
epidote  and  chlorite.  The  vein  trends  approximately  N.  20°  W. 
and  dips  somewhat  irregularly,  from  70°  E.  at  the  surface  to  40°  E. 
on  the  adit  level.  The  walls  are  well  defined;  the  thickness  of  the 
vein  averages  2 feet  on  the  surface  and  5 feet  on  the  adit  level.  In 
places  the  diorite  wall  rock  is  highly  altered  to  a snow-white  rock 
cut  by  quartz  stringers  and  studded  with  numerous  small  perfect 
cubes  of  ])yrite.  The  vein  is  practically  barren  of  metallic  minerals 
but  carries  a small  amount  of  pyrite  and  chalcopyrite. 

Another  vein,  smaller  than  the  Bear  vein,  was  crosscut  by  the 
adit  level  at  300  feet  from  the  portal.  It  is  from  2 to  5 feet  thick, 
strikes  N.  15°  W.,  and  dips  from  10°  to  40°  E.  About  100  feet  of 
drifts  have  been  driven  on  the  ledge. 

KENSINGTON  MINE. 

The  Kensington  mine  is  situated  on  the  north  slope  of  Sherman 
Creek  2 miles  due  east  of  Comet.  During  the  years  1897  to  1900 
some  12,000  tons  of  ore  was  mined  from  the  outcrop  and  from  shallow 
underground  workings.  In  1904  a long  crosscut  tunnel  was  driven 
to  prove  the  persistence  of  the  ore  body  in  depth.  Since  that  time 
no  further  work  has  been  done  on  the  property,  but  on  the  settle- 
ment of  certain  legal  difficulties  it  will  undoubtedly  be  reopened. 

The  portal  of  the  crosscut  tunnel  is  situated  at  an  altitude  of  2,100 
feet  and  is  connected  with  the  gravity  tram  of  the  Bear  mine  by  an 
aerial  tramway,  but  this  is  now  in  a state  of  extreme  disrepair. 
(See  fig.  4.)  The  tunnel,  which  will  serve  as  the  main  working  adit, 
is  1,950  feet  long,  and  drifts  and  crosscuts  aggregating  640  feet  have 
been  driven  to  explore  and  define  the  limits  of  the  ore  body.  The 
up])er  workings  of  the  Kensington  are  situated  at  an  elevation  of  2,800 
feet,  or  800  feet  above  the  crosscut  tunnel.  Here  some  large,  irreg- 
ular galleries  have  been  stoped  out,  in  ])laces  30  feet  high,  but  none  of 
the  tunnels  extend  over  250  feet  into  the  mountain.  Some  mining 
has  also  been  done  on  the  surface  croppings  40  feet  above  the  entrance 
to  the  tunnels. 


DESCRIPTIONS  OF  MINES  AND  PROSPECTS. 


41 


The  geologic  features  of  the  Kensington  ore  body  as  shown  in  the 
outcrop  and  in  the  tunnels  on  both  levels  are  essentially  similar. 
The  ore  body  consists  of  an  irregular  mass  of  diorite  gashed  by  a 
multitude  of  quartz  stringers,  which  range  in  thickness  from  a seam 
to  a foot  but  commonly  average  a few  inches.  In  plan  the  ore  body, 
as  shown  on  the  luain  crosscut  level,  rudely  approximates  an  ellipse 
80  feet  in  width  and  160  feet  in  length,  with  the  major  axis  trending 
north  and  south.  The  two  levels  give  cross  sections  SOO  feet  verti- 
cally apart  and  apparently  show  that  the  deposit  constitutes  an 
inclined  column  or  chimney  of  ore  dipping  67°  E. 

The  quartz  veinlets  in  the  main  interlace  the  diorite  irregularly, 
but  show  an  ill-defined  tendency  to  trend  ])arallel  to  the  major  axis 
of  the  lode  in  cross  section.  They  carry  pyrite  as  the  only  metallic 
mineral  visible  to  the  eye,  though  a small  amount  of  galena  was 
noted  at  one  point.  The  diorite  adjoining  the  quartz  veinlets  is 
heavily  pyritic  in  places,  but  more  commonly  it  contains  scattered 


grains  of  pyrite  disseminated  through  it.  The  diorite  has  not  under- 
gone sufficient  alteration  from  the  action  of  vein-forming  solutions 
to  obscure  its  dioritic  appearance.  Nevertheless  it  differs  notice- 
ably from  the  barren  diorite,  being  in  general  of  a greener  color — a 
change  that  is  due  largely  to  the  conversion  of  the  lustrous  flakes 
of  black  biotite  to  dull-green  chlorite.  The  feldspars  are  sericitized 
and  other  changes  have  taken  place,  described  in  detail  elsewhere  in 
this  report.  The  larger  stringers  are  practically  solid  quartz;  the 
small  veinlets,  especially  those  that  finger  out  into  the  country  rock, 
contain  carbonates,  with  which,  as  shown  by  the  microscope,  is  asso- 
ciated some  albite  feldspar. 

A lam])rophyric  dike  16  inches  thick,  with  strongly  chilled  margins, 
was  encountered  in  the  north  drift  on  the  main  crosscut  level.  It  is 
a dark  fine-textured  jiorphyritic  rock  showing  numerous  pheno- 
crysts  of  hornblende.  Under  the  microscope  hornblende  is  found 
to  be  the  most  abundant  constituent  and  to  form  both  the  pheno- 


42 


THE  BERNERS  BAY  REGION,  ALASKA. 


crysts  and  a large  proportion  of  the  groundmass ; it  is  partly  epi- 
dotized  and  chloritized.  Plagioclase  occurs  interstitially  but  is  ob- 
scured by  sericitization;  some  quartz  is  associated  with  it.  Titanite 
is  a notable  accessory;  magnetite  occurs  sparingly.  Pyrite  and  cal- 
cite  are  sporadic  secondary  minerals.  Such  a rock  would  be  desig- 
nated a spessartite  in  the  classification  of  Rosenbusch.  It  is  prob- 
ably related  to  the  dike  near  the  Portland  mill  described  on  pages 
18-19,  which  was  called  there  a diorite  porphyry  but  which,  as  can 
be  seen  from  the  description,  has  lamprophyric  characteristics.  The 
dike  at  the  Kensington  mine  was  intruded  before  the  ore  body  was 
formed,  so  that  it  is  of  little  practical  significance. 

The  ore  body  is  not  defined  by  walls.  The  values  vary  with  the 
abundance  of  quartz  veinlets  and  are  said  to  range  from  S3  to  $5  a 
ton  for  the  width  of  80  feet.  The  mill  returns  are  reported  to  have 
shown  the  following  distribution  of  values:  Bullion  5 per  cent,  con- 
centrates 62  per  cent,  tailings  33  per  cent. 

EUREKA  MINE. 

The  Eureka  lode  outcrops  several  hundred  feet  below  the  Kensing- 
ton and  has  been  undercut  by  the  Kensington  tunnel  at  a depth  of 
approximately  350  feet  below  the  exposed  outcrop  and  1 ,300  feet  from 
the  mouth  of  the  tunnel.  The  geologic  features  are  essentially  similar 
to  those  of  the  Kensington  ore  body,  but  in  form  the  Eureka  is  longer 
and  narrower.  It  is  400  feet  loaig  on  the  surface  and  where  intersected 
by  the  crosscut  is  from  30  to  40  feet  wide,  consisting  of  a mass  of 
coarse  diorite  closely  interlaced  with  quartz  stringers.  No  drifting 
has  been  done  along  the  lode  on  the  crosscut'  level.  Careful  assays 
across  a width  of  18  feet  are  reported  to  give  a minimum  value  of  $6.56 
a ton  for  the  ore  body  as  exposed  in  the  Kensington  tunnel. 

COMET  MINE. 

The  Comet  mine  is  situated  near  the  head  of  Sherman  Creek,  the 
veins  outcropping  at  an  elevation  of  2,300  feet  and  the  main  crosscut 
entering  the  mountain  at  an  elevation  of  1,650  feet.  The  property 
was  located  in  1890  by  six  owners,  who  sold  it  to  Thomas  Nowell 
in  1892.  Developments  began  in  1893,  the  main  crosscut  was  com- 
menced in  1896,  and  the  property  was  operated  until  1901 ; since  that 
time  it  has  laid  idle,  being  tied  up  by  litigation.  The  improvements 
have  gone  to  ruin,  the  buildings  have  collapsed,  and  the  tunnels  have 
partly  caved  in.  The  underground  developments  were  consequently 
not  accessible  at  the  time  of  visit  in  1909. 

Two  veins  are  exposed  on  the  surface  at  an  elevation  of  2,300  feet. 
They  lie  in  the  diorite  near  the  contact  of  the  slates  and  graywackes 
of  the  Berners  formation,  strike  N.  5°  E.  and  dip  70°  E.  Their  trend 
is  therefore  nearly  at  right  angles  to  the  contact.  The  veins  are  about 


DESCRIPTIONS  OF  MINES  AND  PROSPECTS. 


48 


50  feet  apart;  the  western  one  appears  to  be  the  larger  and  in  the 
outcrop  is  2 to  3 feet  thick,  though  carrying  relatively  large  horses  of 
diorite.  It  is  a well-defined  fissure  vein  and,  as  shown  by  the  lower 
levels,  ranges  up  to  8 feet  in  thickness. 

The  main  crosscut,  which  is  connected  by  an  aerial  tramway  5,000 
feet  long  with  the  40-stamp  Kensington  mill,  is  1,900  feet  long.  It 
traverses  a belt  of  slates,  encountering  a number  of  intruded  dikes  of 
diorite  porphyry,  penetrates  the  main  mass  of  diorite  at  1,500  feet 
from  the  portal,  and  undercuts  the  ore  body  at  approximately  600 
feet  below  the  apex.  The  foot-wall  vein  has  been  stoped  out  from 
this  level  to  the  surface.  Drifts  extending  north  and  south  have  been 
driven  on  ten  different  levels  and  range  in  length  from  300  to  500  feet. 
The  vein  is  faulted  at  the  north  and  its  extension  has  not  yet  been 
recovered. 

The  Comet  vein  is  famous  throughout  the  Juneau  district  for  its 
pockety  character.  Masses  of  golden  quartz  difficult  to  break  in 
mining  were  found,  and  pockets  containing  $50,000  or  more  in  value 
have  been  extracted,  but  it  is  believed  that  much  gold  has  been  lost 
by  ^diigh  grading.”  The  total  recorded  production  is  $460,000,  ex- 
tracted from  50,000  tons  of  ore.  The  ore  yielded  87  per  cent  of  its 
value  in  free  gold  and  5 per  cent  in  the  concentrates. 

JOHNSON  MINE. 

The  Johnson  property  is  situated  lygh  up  on  the  side  of  the  amphi- 
theater at  the  head  of  Johnson  Creek,  but  is  most  easily  reached  by 
means  of  a good  trail  starting  from  the  Sherman  Creek  side  of  the 
divide.  The  developments  consist  of  a number  of  shallow  surface 
cuts  and  a tunnel  situated  at  an  altitude  of  2,500  feet.  The  property 
is  located  near  the  contact  of  the  series  of  amygdaloids  with  the  intru- 
sive diorite,  which  is  coarsely  granular  and  resembles  that  at  the 
Kensington  mine.  The  amygdaloids  have  been  greatly  changed  by 
the  effects  of  the  diorite  intrusion;  they  are  cut  by  innumerable  dike- 
lets  and  have  been  recrystallized,  so  that  the}^  resemble  dark  finely 
granular  diorites,  but  they  contain  numerous  small  white  oval  areas 
representing  former  amygdules. 

The  ore  body  consists  of  shattered  country  rock  penetrated  by 
quartz  stringers,  forming  a huge  stockwork  extending  up  a precipitous 
gulch  from  2,500  feet  to  the  ridge  line  at  an  altitude  of  3,300  feet,  but 
the  upper  portion  is  buried  under  slide  rock.  The  maximum  pyritic 
mineralization  is  exposed  at  the  mouth  of  the  tunnel.  Here  a len- 
ticular mass  of  fractured  and  somewhat  sheared  diorite,  150  feet  long 
and  30  feet  wide,  forms  a compact  body  of  ore  in  which  the  quartz 
stringers  are  closely  spaced  and  heavily  impregnated  with  pyrite. 
The  trend  of  the  deposit  as  exposed  on  the  surface  is  N.  15°  W.  The 
tunnel  bears  N.  69°  W.  and  is  75  feet  long.  The  face  is  in  barren 


44 


THE  BERNERS  BAY  REGION,  ALASKA. 

diorite,  so  tliat  the  tunnel  is  not  calculated  to  develop  this  portion  of 
the  ore  body. 

The  zone  of  mineralization  extends  up  the  gulch  as  a compact 
stringer  lode  6 to  8 feet  thick,  broadening  out  in  places  so  that  the 
individual  stringers  become  widely  spaced.  At  an  altitude  of  2,800 
feet  large,  irregular  bodies  of  quartz  occur  and  veins  and  stringers 
interlace  the  country  rock,  including  both  diorite  and  greenstone, 
through  a width  of  100  feet  or  more.  The  quartz  here  is  nearly  barren 
of  metallic  sulphides,  contrasting  strikingly  in  this  respect  with  the 
large  amount  shown  at  the  portal  of  the  tunnel.  It  is  reported  that 
commercial  sampling  shows  an  ore  body  1 ,500  feet  long  and  from  50 
to  70  feet  wide,  having  a minimum  average  value  of  $3.90  to  the  ton. 

INDIANA  PROPERTY. 

The  Indiana  group,  the  property  of  the  Alaska  Gold  Mining  Com- 
pany, is  situated  on  Johnson  Creek,  three-quarters  of  a mile  northwest 
of  the  Jualin  mine.  It  was  located  in  1896,  after  the  Jualin  had  been 
opened,  and  was  acquired  by  the  company  in  1897.  During  the  latter 
year  most  of  the  present  improvements  were  made.  A 10-stamp  mill 
and  accessory  buildings  were  erected  and  a steel  water  pipe  line  sev- 
eral thousand  feet  in  length  was  laid.  The  mill  has  never  been  oper- 
ated, and  it  and  the  buildings  have  been  demolished  by  winter  snows. 

Three  tunnels  have  been  driven  into  the  diorite  country  rock  in 
the  attempt  to  develop  the  property.  The  lowermost  and  main 
tunnel  is  1,100  feet  long  and  trends  S.  63°  W. ; at  1,000  feet  from  the 
entrance  drifts  aggregating  500  feet  in  length  have  been  driven  to 
the  southeast  and  northwest.  They  follow  a vertical  shear  zone 
approximately  1 0 feet  thick,  along  which  the  diorite  has  been  reduced 
to  a green  schist.  Neither  quartz  veination  nor  other  mineralization 
appears  along  this  zone.  Other  belts  of  schistose  diorite  (one  nearly 
100  ieet  in  width)  have  been  crosscut  by  the  main  tunnel.  They 
let  in  large  quantities  of  surface  water.  A narrow  lode  of  quartz 
stringers  was  encountered  60  feet  from  the  mouth,  but  owing  to  its 
proximity  to  the  surface  it  can  not  be  explored  by  drifting.  The 
quartz  contains  considerable  pyrite,  which  is  crystallized  in  large 
octahedrons,  and  some  chalcopyrite.  A second  tunnel  100  feet  above 
the  lower  tunnel  is  900  feet  long,  and  the  uppermost,  100  feet  still 
higher,  is  400  feet  long;  but  neither  has  encountered  any  ore. 

JUALIN  MINE. 

The  Jualin  mine  is  situated  on  Johnson  Creek  at  an  altitude  of  750 
feet,  and  is  connected  with  tidewater  at  the  head  of  Berners  Bay 
by  a horse  tramway  4 miles  long.  Supplies  can  be  lightered  at  high 
tide  from  deep  water  in  Jualin  Cove  to  the  wharf  at  the  terminus  of 
the  tramway.  The  mine  was  located  in  1896  by  Frank  Cook  and 


DESCRIPTIONS  OF  MINES  AND  PROSPECTS. 


45 


was  purchased  in  the  same  year  by  the  Jualiii  Mines  Coni})any,  wJiich 
opened  the  property  and  operated  the  mine  continuously  until  1901. 
By  that  time  the  larger  part  of  the  ore  lying  above  the  adit  level  had 
been  worked  out,  and  deeper  development  was  effected  by  winzes 
sunk  from  drifts  on  the  drainage  level.  Heavy  inflow  of  surface 
water  impeded  the  extraction  of  the  ore  on  the  deeper  levels,  and  the 
mine  has  been  operated  only  intermittently  since  1901.  In  1905 
the  tramway  was  built  to  facilitate  transportation  to  the  mine. 
During  1909  the  mine  was  idle,  but  it  is  now  planned  to  develop  the 
property  systematically.  With  this  end  in  view  it  is  proposed  to 
sink  a shaft  during  1910  in  the  hanging-wall  side  of  the  lode. 

A 10-stamp  mill  equipped  with  Frue  vanners  and  operated  by 
water  power  is  situated  on  the  bank  of  Johnson  Creek  below  the 
portal  of  the  working  adit  of  the  mine. 

The  apex  of  an  ore  body  on  the  Jualin  property  was  discovered 
outcropping  in  a rounded,  glacially  smoothed  knob  of  diorite  pro- 
jecting through  the  mat  of  moss  and  vegetation  that  generally 
obscures  all  bed  rock  in  the  valley  of  Johnson  Creek.  The  country 
rock  at  the  Jualin  mine  is  a massive  diorite  of  fairly  fine  grain  and  is 
composed  of  plagioclase  feldspar,  small  prisms  of  hornblende,  and 
flakes  of  biotite.  Even  in  the  freshest  looking  rock  many  of  the 
feldspars  can  be  seen  to  have  a delicate  green  tint.  In  addition  to 
these  minerals,  which  are  visible  to  the  eye,  the  microscope  shows  that 
orthoclase  and  quartz  are  present  in  some  amount  and  that  therefore 
the  rock  approaches  a granodiorite  in  composition.  The  rock  has 
evidently  been  permeated  by  mineral-bearing  solutions,  and  owing 
to  the  chemical  activity  of  those  waters  the  jirimary  minerals  have 
suffered  considerable  alteration.  Epidote,  chlorite,  the  scaly  green 
mica  sericite,  and  calcite  have  been  formed  at  their  expense.  This 
alteration  is  of  course  most  ])ronounced  in  proximity  to  the  veins, 
where  in  some  places  a complete  transformation  of  the  diorite  has 
occurred,  and  none  of  the  original  minerals  have  remained  intact. 

Three  parallel  veins  spaced  75  feet  apart  on  the  adit  level  have  been 
exploited.  They  trend  N.  40°  W.  and  dip  steeply  to  the  northeast 
at  angles  ranging  from  60°  to  90°.  The  foot-wall  or  west  vein,  as 
it  is  called,  has  proved  to  be  the  most  valuable.  It  has  been  exposed 
for  400  feet  in  length  and  has  averaged  5 feet  in  width.  It  has  been 
developed  by  winzes  to  a depth  of  200  feet  below  the  adit  level.  At 
the  southeast  end  of  the  drift  on  the  adit  level  the  vein  has  com- 
pletely pinched  out.  and  the  diorite  at  the  face  is  firm  and  massive; 
before  pinching,  the  dip  is  abruptly  reversed  to  a flatter  angle  and 
the  vein  apparently  loses  itself  in  a zone  of  crushed  diorite.  About 
50  feet  to  the  northwest  along  the  trend  the  vein  is  16  to  24  inches 
thick  and  the  hanging  wall  is  splendidly  defined,  dipping  steeply  to  the 
northeast ; the  foot-wall  is  marked  by  a closely  foliated  green  schist 


46 


THE  BERNERS  BAY  REGION,  ALASKA. 


produced  by  the  mashing  of  the  diorite.  That  this  crushing  took 
place  prior  to  the  tilling  of  the  vein  is  proved  by  the  fact  that  the 
quartz  near  the  foot-wall  incloses  fragments  of  the  schist.  From  this 
point  the  vein  abruptly  expands  to  10  feet  in  width.  Part  of  this 
increased  thickness  seems  to  be  due  to  movement  along  a fault  plane 
traversing  the  vein  at  a narrow  angle  with  the  trend  of  the  vein. 
Faults  of  small  displacement  have  been  encountered  at  other  points 
in  the  mine,  but  have  occasioned  no  difficulties  in  the  exploitation  of 
the  ore  bodies. 

The  middle  vein  as  exposed  in  the  main  adit  shows  well-defined 
walls,  which  break  clean,  but  the  vein  is  only  18  inches  thick  at  this 
point  and  consists  of  quartz  and  partly  replaced  diorite.  The  dip  is 
rather  flat — 30°  N.  More  or  less  shattered  country  rock  adjoins  the 
vein  and  is  penetrated  by  sporadic  stringers  of  quartz.  The  next  120 
feet  of  the  adit  is  driven  on  a shear  zone  of  irregular  width  ranging 
from  4 to  8 feet;  quartz  is  present  only  as  stringers.  The  dip  of  the 
ore  body  gradually  steepens,  and  at  120  feet  a large  body  of  quartz  was 
encountered  which  averaged  10  feet  in  width  throughout  its  length 
of  400  feet.  This  vein  has  yielded  several  thousand  tons  of  ore  in 
past  years,  but  its  value  is  said  to  be  too  low  to  warrant  further 
extraction. 

The  third  or  hanging-wall  vein  is  4 to  5 feet  thick  and  is  of  some- 
what better  grade  than  the  second  ore  body.  It  is  characterized  by 
a clean,  well-defined  hanging  wall,  but  the  foot-wall  is  less  regular 
and  is  reticulated  by  a considerable  number  of  quartz  veinlets,  which 
are  accompanied  by  an  impregnation  of  the  diorite  with  cubical 
pyrite. 

The  quartz  of  the  veins  is  of  milk-white  color  and  open  texture 
and  is  characterized  by  the  presence  of  numerous  druses  or  small 
vugs,  into  which  terminated  fjuartz  crystals  project.  Metallic  sul- 
phides are  present  in  considerable  abundance  and  consist  mainly  of 
pyrite,  chalco])yrite,  and  galena.  Black  sphalerite  occurs  also,  but  is 
extremely  rare.  Free  gold  is  not  uncommon  and  seems  to  be  asso- 
ciated particularly  with  the  chalcopyrite,  in  which  it  is  usually 
embedded.  The  ore  and  wall  rock  show  to  some  extent  the  oxidizing 
effect  of  surface  waters,  as  indicated  by  the  presence  of  red  iron 
ocher  and  of  malachite  and  azurite,  though  the  copper  carbonates 
are  comparatively  rare.  Free  gold  can  be  found  here  and  there  in  the 
midst  of  small  masses  of  iron  oxide,  where  it  has  undoubtedly  been 
freed  by  the  oxidation  of  the  pyritic  mineral  that  originally  inclosed  it. 

The  oxidation  affecting  the  upper  parts  of  the  lodes  is  of  postglacial 
origin  and  is  comparatively  feeble.  The  products  of  any  earlier 
oxidation  and  enrichment  of  the  outcrops  of  the  lodes  have  been 
swept  aw^ay  by  the  pow^erful  glacial  erosion  to  wffiich  the  region  w^as 
subjected.  These  facts — the  lack  of  oxidation  and  the  glacial 


DESCKIPTIONS  OF  MINES  AND  PROSPECTS. 


47 


erosion— make  it  probable  that  tlie  distribution  of  the  gold  in  the 
veins  has  undergone  only  slight  rearrangement  from  the  action  of 
descending  solutions  and  that  therefore  the  tenor  of  the  ore  is  not 
likely  to  decrease  with  depth. 

FREMMING  PROPERTY. 

The  Fremming  property  is  situated  on  Johnson  Creek  about  a mile 
below  the  Jualin  mine.  The  valley  floor  at  this  point  is  mantled  by 
several  feet  of  gravel  and  black  soil  covered  with  sod.  Stripping 
shows  that  the  bed  rock  is  glacially  polished  and  striated.  Near  the 
blacksmith  shop  an  intrusion  contact  of  the  Jualin  diorite  with  a 
series  of  green  schists  is  exposed.  Small  dikes  of  diorite  penetrate 
the  schist,  which,  if  the  relations  were  not  clearly  shown,  might  be 
regarded  as  a chloritic  schist  produced  by  dynamic  metamorphism 
of  the  diorite  itself.  Both  the  diorite  and  the  green  schist  are  inter- 
laced with  irregular  quartz  stringers. 

A shaft  85  feet  deep  has  been  sunk  near  the  contact  in  the  green 
schists.  The  main  development  consists  of  a crosscut  tunnel  360 
feet  long,  commencing  on  the  east  bank  of  Johnson  Creek  and  trend- 
ing N.  28°  E.  A short  drift  connects  the  crosscut  tunnel  with  the 
bottom  of  the  shaft.  The  tunnel  crosscuts  a nearly  vertical  series 
of  green  schists.  These  are  derived  from  slates  and  graywacke- 
slates  of  the  Berners  formation  and  owe  their  stronger  green  color 
to  a greater  abundance  of  chlorite  in  them.  Near  the  end  of  the  cross- 
cut a belt  of  schists  is  irregularly  penetrated  by  stringers  across  a 
width  of  6 feet.  The  veinlets  and  j)artly  replaced  chloritic  rock 
consist  of  quartz  and  calcite  containing  yiyrite,  chalcopyrite,  galena, 
resinous  sphalerite,  and  free  gold . Eich  specimen  ore  can  be  obtained, 
but  the  present  developments  are  inadecpiate  to  show  wliether  a body 
of  milling  ore  exists. 

GREEK  BOY  PROPERTY. 

The  Greek  Boy  jiroperty  is  situated  4 miles  north  of  the  tidewater 
terminus  of  the  Jualin  tramway  and  half  a mile  from  Berners  River. 
It  is  the  lowest  lying  property  in  the  region,  the  principal  workings 
being  only  100  feet  above  sea  level. 

The  main  development  consists  of  a tunnel  nearW  700  feet  long, 
trending  northwest.  For  the  first  few  hundred  feet  it  makes  a narrow 
angle  with  the  strike  of  the  lode ; the  last  300  feet  is  driven  on  the  lode. 
The  ore  body  follows  the  contact  of  the  quartz  diorite  gneiss  with 
the  basalts,  which  are  here  thoroughly  schistose,  and  is  a strong 
stringer  lode  bounded  by  definite  walls.  It  stands  nearly  vertical, 
dipping  steeply  to  the  south.  The  hanging  wall  is  a black  horn- 
blende schist,  wdiich  the  microscope  shows  to  be  composed  mainly 
of  hornblende  and  some  plagioclase. 


48 


THE  BERNERS  BAY  REGION,  ALASKA. 


The  first  rock  encountered  on  entering  the  tunnel  is  a gneissic  or 
schistose  diorite  consisting  of  numerous  white  rounded  feldspars 
embedded  in  a black  matrix  made  up  of  hornblende  and  biotite. 
With  increasing  proximity  to  the  lode  this  rock  becomes  finer  grained 
and  nearly  barren  of  dark  rninerals.  As  the  lode  lies  along  the 
contact  of  an  intruded  formation,  this  change  means  that  the  rock  is 
a marginal  phase  of  the  diorite,  a change  noted  in  other  parts  of  the 
field  where  it  is  not  obscured,  as  it  is  here,  by  the  subsequent  altera- 
tions produced  by  vein-forming  solutions. 

The  lode  consists  of  the  schistose  marginal  phase  of  the  diorite 
reticulated  with  cpiartz  stringers,  forming  in  places  an  ore  body  of 
nearly  solid  quartz.  At  other  places  considerable  country  rock  is 
included  in  the  lode.  The  thickness  ranges  from  4 to  9 feet  and 
averages  perhaps  7 feet.  The  only  metallic  mineral  noted  in  the 
quartz  is  pyrite,  and  this  is  present  in  sparse  amount  only. 


RECENT  SURVEY  PUBLICATIONS  ON  ALASKA. 

[Arranged  geographically.  A complete  list  can  be  had  on  application.] 

All  these  publications  can  be  obtained  or  consulted  in  the  following  ways: 

1.  A limited  number  are  delivered  to  the  Director  of  the  Survey,  from  whom  they 
can  be  obtained  free  of  charge  (except  certain  maps)  on  application. 

2.  A certain  number  are  delivered  to  Senators  and  Representatives  in  Congress  for 
distribution. 

3.  Other  copies  are  deposited  with  the  Superintendent  of  Documents,  Washington, 
D.  C.,  from  whom  they  can  be  had  at  prices  slightly  above  cost.  The  publications 
marked  with  an  asterisk  (*)  in  this  list  are  out  of  stock  at  the  Survey,  but  can  be 
purchased  from  the  Superintendent  of  Documents  at  the  prices  stated. 

4.  Copies  of  all  government  publications  are  furnished  to  the  principal  public 
libraries  throughout  the  United  States,  where  they  can  be  consulted  by  those  inter- 
ested. 

GENERAL. 

*The  geography  and  geology  of  Alaska,  a summary  of  existing  knowledge,  by  A.  H. 
Brooks,  with  a section  on  climate,  by  Cleveland  Abbe,  jr.,  and  a topographic 
map  and  description  thereof,  by  R.  U.  Goode.  Professional  Paper  45,  1906, 
327  pp.  $1. 

Placer  mining  in  Alaska  in  1904,  by  A.  H.  Brooks.  In  Bulletin  259,  1905,  pp.  18-31. 
The  mining  industry  in  1905,  by  A.  H.  Brooks.  In  Bulletin  284,  1906,  pp.  4-9. 
The  mining  industry  in  1906,  by  A.  II.  Brooks.  In  Bulletin  314,  1907,  pp.  19-39. 
*The  mining  industry  in  1907,  by  A.  II.  Brooks.  In  Bulletin  345,  pp.  30-53.  45  cents. 

The  mining  industry  in  1908,  by  A.  II.  Brooks.  In  Bulletin  379,  1909,  pp.  21-62. 
The  mining  industry  in  1909,  by  A.  IT.  Brooks.  In  Bulletin  442,  1910,  pp.  20-46. 
Railway  routes,  by  A.  H.  Brooks.  In  Bulletin  284,  1906,  pp.  10-17. 

Administrative  report,  by  A.  II.  Brooks.  In  Bulletin  259,  1905,  pp.  13-17. 

Administrative  report,  by  A.  II.  Brooks.  In  Bulletin  284,  1906,  pp.  1-3. 

Administrative  report,  by  A.  II.  Brooks.  In  Bulletin  314,  1907,  pp.  11-18. 

*Administrative  report,  by  A.  II.  Brooks.  In  Bulletin  345,  1908,  pp.  5-17.  45  cents. 

Administrative  report,  by  A.  H.  Brooks.  In  Bulletin  379,  1909,  pp.  5-20. 

Administrative  report,  by  A.  H.  Brooks.  In  Bulletin  442,  1910,  pp.  5-19. 

Notes  on  the  petroleum  fields  of  Alaska,  by  G.  C.  Martin.  In  Bulletin  259,  1905, 
pp.  128-139. 

The  petroleum  fields  of  the  Pacific  Coast  of  Alaska,  with  an  account  of  the  Bering 
River  coal  deposits,  by  G.  C.  Martin.  Bulletin  250,  1905,  64  pp. 

Markets  for  Alaska  coal,  by  G.  C.  Martin.  In  Bulletin  284, 1906,  pp.  18-29. 

The  Alaska  coal  fields,  by  G.  C.  Martin.  In  Bulletin  314,  1907,  pp.  40-M6. 

Alaska  coal  and  its  utilization,  by  A.  II.  Brooks.  In  Bulletin  442,  1910,  pp.  47-100. 
The  possible  use  of  peat  fuel  in  Alaska,  by  C.  A.  Davis.  In  Bulletin  379,  1909, 
pp.  63-66. 

The  preparation  and  use  of  peat  as  a fuel,  by  C.  A.  Davis.  In  Bulletin  442,  1910, 
pp.  101-132. 

*The  distribution  of  mineral  resources  in  Alaska,  by  A.  H.  Brooks.  In  Bulletin  345, 
pp.  18-29.  45  cents. 

Mineral  resources  of  Alaska,  by  A.  H.  Brooks.  In  Bulletin  394,  1909,  pp.  172-207. 
^Methods  and  costs  of  gravel  and  placer  mining  in  Alaska,  by  C.  W.  Purington. 

Bulletin  263, 1905,  362  pp.  35  cents.  Abstract  in  Bulletin  259, 1905,  pp.  32-46. 
^Prospecting  and  mining  gold  placers  in  Alaska,  by  J.  P.  Hutchins.  In  Bulletin 
345,  1908,  pp.  54-77.  45  cents. 

Geographic  dictionary  of  Alaska,  by  Marcus  Baker;  second  edition  by  James  McCor- 
mick. Bulletin  299,  1906,  690  pp. 

*Water-supply  investigations  in  Alaska  in  1906-7,  by  F.  F.  Henshaw  and  C.  C. 
Covert.  Water-Supply  Paper  218,  1908,  156  pp.  25  cents. 

67811°— Bull.  446—11 4 


49 


50 


SURVEY  PUBLICATIONS  ON  ALASKA. 


Topographic  maps. 

Alaska,  topographic  map  of;  scale,  1 : 2,500,000;  preliminary  edition;  by  R.  U. 

Goode.  Contained  in  Professional  Paper  45.  Not  published  separately. 

Map  of  Alaska  showing  distribution  of  mineral  resources;  scale,  1 ; 5,000,000;  by 
A.  H.  Brooks.  Contained  in  Bulletin  345  fin  pocket). 

Map  of  Alaska;  scale,  1 : 5,000,000;  by  Alfred  H.  Brooks. 

SOUTHEASTERN  ALASKA. 

^Preliminary  report  on  the  Ketchikan  mining  district,  Alaska,  with  an  introductory 
sketch  of  the  geology  of  southeastern  Alaska,  by  Alfred  H.  Brooks.  Professional 
Paper  .1,  1902,  120  pp.  25  cents. 

*The  Porcupine  placer  district,  Alaska,  by  C.  W.  Wright.  Bulletin  236,  1904,  35  pp. 
15  cents. 

The  Treadwell  ore  deposits,  by  A.  C.  Spencer.  In  Bulletin  259,  1905,  pp.  69-87. 
Economic  developments  in  southeastern  Alaska,  by  F.  E.  and  C.  W,  Wright.  In 
Bulletin  259,  1905,  pp.  47-68. 

The  Juneau  gold  belt,  Alaska,  by  A.  C.  Spencer,  pp.  1-137,  and  A reconnaissance  of 
Admiralty  Island,  Alaska,  by  C.  W.  Wright,  pp.  138-154.  Bulletin  287,  1906, 

161  pp. 

Lode  mining  in  southeastern  Alaska,  by  F.  E.  and  C.  W.  Wright.  In  Bulletin  284, 
1906,  pp.  30-53. 

Nonmetallic  deposits  of  southeastern  Alaska,  by  C.  W.  Wright.  In  Bulletin  284, 
1906,  pp.  54-60. 

The  Yakutat  Bay  region,  by  R.  S.  Tarr.  In  Bulletin  284,  1906,  pp.  61-64. 

Lode  mining  in  southeastern  Alaska,  by  C.  W.  Wright.  In  Bulletin  314,  1907, 
pp.  47-72. 

Nonmetalliferous  mineral  resources  of  southeastern  Alaska,  by  C.  W.  Wright.  In 
Bulletin  314,  1907,  pp.  73-81. 

Reconnaissance  on  the  Pacific  coast  from  Yakutat  to  Alsek  River,  by  Eliot  Black- 
welder.  In  Bulletin  314,  1907,  pp.  82-88. 

*Lode  mining  in  southeastern  Alaska  in  1907,  by  C.  W.  Wright.  In  Bulletin  345, 
1908,  pp.  78-97.  45  cents. 

*The  building  stones  and  materials  of  southeastern  Alaska,  by  C.  W.  Wright.  In 
Bulletin  345,  1908,  pp.  116-126.  45  cents. 

*Copper  deposits  on  Kasaan  Peninsula,  Prince  of  Wales  Island,  by  C.  W.  Wright  and 
Sidney  Paige.  In  Bulletin  345,  1908,  pp.  98-115.  45  cents. 

The  Ketchikan  and  Wrangell  mining  districts,  Alaska,  by  F.  E.  and  C.  W.  Wright. 
Bulletin  347,  1908,  210  pp. 

The  Yakutat  Bay  region,  Alaska:  Physiography  and  glacial  geology,  by  R.  S.  Tarr; 
Areal  geology,  by  R.  S.  Tarr  and  B.  S.  Butler.  Professional  Paper  64,  1909, 

186  pp. 

Mining  in  southeastern  Alaska,  by  C.  W.  Wright.  In  Bulletin  379,  1909,  pp.  67-86. 
Mining  in  southeastern  Alaska,  by  Adolph  Knopf.  In  Bulletin  442,  1910,  pp.  133- 
143. 

The  occurrence  of  iron  ore  near  Haines,  by  Adolph  Knopf.  In  Bulletin  442,  1910, 
pp.  144-146. 

A water-power  reconnaissance  in  southeastern  Alaska,  by  J.  C.  Hoyt.  In  Bulletin 
442,  1910,  pp.  147-157. 


Topographic  maps. 

Juneau  special  quadrangle;  scale,  1 : 62,500;  by  W.  J.  Peters.  For  sale  at  5 cents 
each  or  $3  per  hundred. 

Berners  Bay  special  map;  scale,  1 : 62,500;  by  R.  B.  Oliver.  For  sale  at  5 cents 
each  or  $3  per  hundred. 

Topographic  map  of  the  Juneau  gold  belt,  Alaska.  Contained  in  Bulletin  287, 
Plate  XXXVI,  1906.  Not  issued  separately. 

In  preparation. 

The  Yakutat  Bay  earthquake  of  September,  1899,  by  R.  S.  Tarr  and  Lawrence 
Martin.  Professional  Paper  69. 

Kasaan  Peninsula  special  map;  scale,  1 : 62,500;  by  D.  C.  Witherspoon,  J.  W. 
Bagley,  and  R.  11.  Sargent. 

Copper  Mountain  special  map;  scale,  1 : 62,500;  by  R.  II.  Sargent. 


SUKVEY  PUBLICATIONS  ON  ALASKA. 


51 


CONTROLLER  BAY.  PRINCE  WILLIAM  SOUND,  AND  COPPER  RIVER  REGIONS. 

*The  mineral  resources  of  the  Mount  Wrangell  district,  Alaska,  by  W.  C.  Mendenhall. 
Professional  Paper  15,  1903,  71  pp.  Contains  general  map  of  Prince  William 
Sound  and  Copper  River  region;  scale,  12  miles  =1  inch.  30  cents. 

Bering  River  coal  field,  by  G.  C.  Martin.  In  Bulletin  259,  1905,  pp.  140-150. 

Cape  Yaktag  placers,  by  G.  C.  Martin.  In  Bulletin  259,  1905,  pp.  88-89.  | 

Notes  on  the  petroleum  fields  of  Alaska,  by  G.  C.  Martin.  In  Bulletin  259,  1905, 
pp.  128-139.  Abstract  from  Bulletin  250. 

The  petroleum  fields  of  the  Pacific  coast  of  Alaska,  with  an  account  of  the  Bering 
River  coal  deposits,  by  G.  C.  Martin.  Bulletin  250,  1905,  64  pp. 

Geology  of  the  central  Copper  River  region,  Alaska,  by  W.  C.  Mendenhall.  Profes- 
sional Paper  41,  1905,  133  pp. 

Copper  and  other  mineral  resources  of  Prince  William  Sound,  by  U.  S.  Grant.  In 
Bulletin  284,  1906,  pp.  78-87. 

Distribution  and  character  of  the  Bering  River  coal,  by  G.  C.  Martin.  In  Bulletin 
284,  1906,  pp.  65-76. 

Petroleum  at  Controller  Bay,  by  G.  C.  Martin.  In  Bulletin  314,  1907,  pp.  89-103. 
Geology  and  mineral  resources  of  Controller  Bay  region,  by  G.  C.  Martin.  Bulletin 
335, 1908,  141  pp. 

* Notes  on  copper  prospects  of  Prince  William  Sound,  by  F.  H.  Moffit.  In  Bulletin 

345,  1908,  pp.  176-178.  45  cents. 

* Mineral  resources  of  the  Kotsina  and  Chitina  valleys.  Copper  River  region,  by  F.  H. 

Moffit  and  A.  G.  Maddren.  In  Bulletin  345,  1908,  pp.  127-175.  45  cents. 
Mineral  resources  of  the  Kotsina-Chitina  region,  by  F.  H.  Moffit  and  A.  G.  Maddren. 
Bulletin  374,  1909,  103  pp. 

Copper  mining  and  prospecting  on  Prince  William  Sound,  by  U.  S.  Grant  and  D.  F. 

Higgins,  jr.  In  Bulletin  379,  1909,  pp.  87-96. 

Gold  on  Prince  William  Sound,  by  U.  S.  Grant.  In  Bulletin  379,  1909,  p.  97. 
Mining  in  the  Kotsina-Chitina,  Chistochina,  and  Valdez  Creek  regions,  by  F.  H. 

Moffit.  In  Bulletin  379,  1909,  pp.  153-160. 

Mineral  resources  of  the  Nabesna- White  River  district,  by  F.  H.  Moffit  and  Adolph 
Knopf.  In  Bulletin  379,  1909,  pp.  161-180. 

Mineral  resources  of  the  Nabesna-White  River  district,  by  F.  H.  Moffit  and  Adolph 
Knopf;  with  a section  on  the  Quaternary,  by  S.  R.  Capps.  Bulletin  417,  1910, 
64  pp. 

Mining  in  the  Chitina  district,  by  F.  H.  Moffit.  In  Bulletin  442,  1910,  pp.  158-163. 
Mining  and  prospecting  on  Prince  William  Sound,  by  U.  S.  Grant.  In  Bulletin 
442,  1910,  pp.  164-165. 

Reconnaissance  of  the  geology  and  mineral  resources  of  Prince  William  Sound, 
Alaska,  by  U.  S.  Grant  and  D.  F.  Higgins.  Bulletin  443,  1910,  89  pp. 

Topographic  maps. 

Map  of  Mount  Wrangell;  scale,  12  miles  =1  inch.  Contained  in  Professional  Paper 
15.  Not  issued  separately. 

Copper  and  upper  Chistochina  rivers;  scale,  1:250,000;  by  T.  G.  Gerdine.  Con- 
tained in  Professional  Paper  41.  Not  issued  separately. 

Copper,  Nabesna,  and  Chisana  rivers,  headwaters  of;  scale,  1: 250,000;  by  D.  C.  With- 
erspoon. Contained  in  Professional  Paper  41.  Not  issued  separately. 
Controller  Bay  region  special  map;  scale,  1:62,500;  by  E.  G.  Hamilton.  For  sale  at 
35  cents  a copy  or  $21  per  hundred. 

General  map  of  Alaska  coast  region  from  Yakutat  Bay  to  Prince  William  Sound ; scale, 
1:1,200,000;  compiled  by  G.  C.  Martin.  Contained  in  Bulletin  335. 

In  press. 

Geology  and  mineral  resources  of  the  Nizina  district,  by  F.  H.  Moffit  and  S.  R. 
Capps.  Bulletin  448. 

In  preparation. 

Chitina  quadrangle  map;  scale,  1:  250,000;  by  T.  G.  Gerdine  and  D.  C.  Witherspoon. 

COOK  INLET  AND  SUSITNA  REGION. 

The  petroleum  fields  of  the  Pacific  coast  of  Alaska,  with  an  account  of  the  Bering 
River  coal  deposits,  by  G.  C.  Martin.  Bulletin  250,  1905,  64  pp. 

Coal  resources  of  southwestern  Alaska,  by  R.  W.  Stone.  In  Bulletin  259,  1905, 
pp.  151-171, 


52 


SURVEY  PUBLICATIONS  ON  ALASKA. 


Gold  placers  of  Turnagain  Arm,  Cook  Inlet,  by  F.  H.  Moffit.  In  Bulletin  259,  1905, 
pp.  90-99. 

Mineral  resources  of  the  Kenai  Peninsula;  Gold  fields  of  the  Turnagain  Arm  region, 
by  F.  H.  Moffit,  pp.  1-52;  coal  fields  of  the  Kachemak  Bay  region,  by  R.  W. 
Stone,  pp.  53-73.  Bulletin  277,  1906,  80  pp. 

Preliminary  statement  on  the  Matanuska  coal  field,  by  G.  C.  Martin.  In  Bulletin 
284,  1906,  pp.  88-100. 

*A  reconnaissance  of  the  Matanuska  coal  field,  Alaska,  in  1905,  by  G.  C.  Martin. 
Bulletin  289,  1906,  36  pp. 

Reconnaissance  in  the  Matanuska  and  Talkeetna  basins,  by  Sidney  Paige  and 
Adolph  Knopf.  In  Bulletin  314,  1907,  pp.  104-125. 

Geologic  reconnaissance  in  the  Matanuska  and  Talkeetna  basins,  Alaska,  by  Sidney 
Paige  and  Adolph  Knopf.  Bulletin  327,  1907,  71  pp. 

Notes  on  geology  and  mineral  prospects  in  the  vicinity  of  Seward,  Kenai  Peninsula, 
by  U.  S.  Grant.  In  Bulletin  379,  1909,  pp.  98-107. 

Preliminary  report  on  the  mineral  resources  of  the  southern  part  of  Kenai  Peninsula, 
by  U.  S.  Grant  and  D.  F.  Higgins.  In  Bulletin  442,  1910,  pp.  166-178. 

Outline  of  the  geology  and  mineral  resources  of  the  Iliamna  and  Clark  lakes  region 
by  G.  C.  Martin  and  F.  J.  Katz.  In  Bulletin  442,  1910,  pp.  179-200. 

Gold  placers  of  the  Mulchatna,  by  F.  J.  Katz.  In  Bulletin  442,  1910,  pp.  201-202. 

Topographic  maps. 

Kenai  Peninsula,  northern  portion;  scale,  1:250,000;  by  E.  G.  Hamilton.  Con- 
tained in  Bulletin  277.  Not  published  separately. 

Reconnaissance  map  of  Matanuska  and  Talkeetna  region;  scale,  1:250,000;  by 
T.  G.  Gerdine  and  R.  H.  Sargent.  Contained  in  Bulletin  327.  Not  published 
separately. 

Mount  McKinley  region;  scale,  1:625,000;  by  D.  L.  Reaburn.  Contained  in  Pro- 
fessional Paper  45.  Not  published  separately. 

In  press. 

The  Mount  McKinley  region,  by  A.  H.  Brooks,  with  descriptions  of  the  igneous 
rocks  and  of  the  Bonnifield  and  Kantishna  districts,  by  L.  M.  Prindle.  Pro- 
fessional Paper  70. 

SOUTHWESTERN  ALASKA. 

Gold  mine  on  Unalaska  Island,  by  A.  J.  Collier.  In  Bulletin  259,  1905,  pp.  102-103. 

Gold  deposits  of  the  Shumagin  Islands,  by  G.  C.  Martin.  In  Bulletin  259,  1905, 

pp.  100-101. 

Notes  on  the  petroleum  fields  of  Alaska,  by  G.  C.  Martin.  In  Bulletin  259,  1905, 
pp.  128-139.  Abstract  from  Bulletin  250. 

The  petroleum  fields  of  the  Pacific  coast  of  Alaska,  with  an  account  of  the  Bering 
River  coal  deposits,  by  G.  C.  Martin.  Bulletin  250,  1905,  64  pp. 

Coal  resources  of  southwestern  Alaska,  by  R.  W.  Stone.  In  Bulletin  259,  1905, 
pp.  151-171. 

The  Herendeen  Bay  coal  fields,  by  Sidney  Paige.  In  Bulletin  284,  1906,  pp.  101-108. 

Mineral  resources  of  southwestern  Alaska,  by  W.  W.  Atwood.  In  Bulletin  379, 
1909,  pp.  108-152. 

In  preparation. 

Geology  and  mineral  resources  of  parts  of  Alaska  Peninsula,  by  W.  W.  Atwood. 

YUKON  BASIN. 

The  coal  resources  of  the  Yukon,  Alaska,  by  A.  J.  Collier.  Bulletin  218,  1903,  71  pp. 
15  cents. 

*The  gold  placers  of  the  Fortymile,  Birch  Creek,  and  Fairbanks  regions,  by  L.  M. 
Prindle.  Bulletin  251,  1905,  89  pp.  35  cents. 

Yukon  placer  fields,  by  L.  M.  Prindle.  In  Bulletin  284,  1906,  pp.  109-131. 

Reconnaissance  from  Circle  to  Fort  Hamlin,  by  R.  W.  Stone.  In  Bulletin  284,  1906, 
pp.  128-131. 

The  Yukon-Tanana  region,  Alaska;  description  of  the  Circle  quadrangle,  by  L.  M. 
Prindle.  Bulletin  295,  1906,  27  pp. 

The  Bonnifield  and  Kantishna  regions,  by  L.  M.  Prindle.  In  Bulletin  314,  1907, 
pp.  205-226. 

The  Circle  precinct,  Alaska,  by  A.  II . Brooks,  In  Bulletin  314,  1907,  pp.  187-204, 


SURVEY  PUBLICATIONS  ON  ALASKA. 


53 


The  Yukon-Tanana  region,  Alaska;  description  of  the  Fairbanks  and  Rampart  quad- 
rangles, by  L.  M.  Prindle,  F.  L.  Hess,  and  C.  C.  Covert.  Bulletin  337,  1908, 

102  pp. 

*Occurrence  of  gold  in  the  Yukon-Tanana  region,  by  L.  M.  Prindle.  In  Bulletin 
345,  1908,  pp.  179-186.  45  cents. 

*The  Fortymile  gold-placer  district,  by  L.  M.  Prindle.  In  Bulletin  345, 1908,  pp.  187- 
197.  45  cents. 

Water-supply  investigations  in  Alaska,  1906  and  1907,  by  F.  F.  Henshaw  and  C.  C. 
Covert.  Water-Supply  Paper  218,  1908,  156  pp. 

*Water  supply  of  the  Fairbanks  district  in  1907,  by  C.  C.  Covert.  In  Bulletin  345, 
1908,  pp.  198-205.  45  cents. 

The  Fortymile  quadrangle,  by  L.  M.  Prindle.  Bulletin  375,  1909,  52  pp. 

Water-supply  investigations  in  Yukon-Tanana  region,  1906-1908,  by  C.  C.  Covert 
and  C.  E.  Ellsworth.  Water-Supply  Paper  228,  1909,  108  pp. 

The  Fairbanks  gold-placer  region,  by  L.  M.  Prindle  and  F.  J.  Katz.  In  Bulletin 
379,  1909,  pp.  181-200. 

Water  supply  of  the  Yukon-Tanana  region,  1907-8,  by  C.  C.  Covert  and  C.  E.  Ells- 
worth. In  Bulletin  379,  1909,  pp.  201-228. 

Gold  placers  of  the  Ruby  Creek  district,  by  A.  G.  Maddren.  In  Bulletin  379,  1909, 
pp.  229-233. 

Placers  of  the  Gold  Hill  district,  by  A.  G.  Maddren.  In  Bulletin  379,  1909,  j:>p.  234- 
237. 

Gold  placers  of  the  Innoko  district,  by  A.  G.  Maddren.  In  Bulletin  379,  1909, 
pp.  238-26^. 

The  Innoko  gold-placer  district,  with  accounts  of  the  central  Kuskokwim  Valley  and 
the  Ruby  Creek  and  Gold  Hill  placers,  by  A.  G.  Maddren.  Bulletin  410,  1910, 
87  pp. 

Sketch  of  the  geology  of  the  northeastern  part  of  the  Fairbanks  quadrangle,  by 
L.  M.  Prindle.  In  Bulletin  442,  1910,  pp.  203-209. 

The  auriferous  quartz  veins  of  the  Fairbanks  district,  by  L.  M.  Prindle.  In  Bulletin 
442,  1910,  pp.  210-229. 

Placer  mining  in  the  Yukon-Tanana  region,  by  C.  E.  Ellsworth.  In  Bulletin  442, 
1910,  pp.  230-245. 

Occurrence  of  wolframite  and  cassiterite  in  the  gold  placers  of  Deadwood  Creek, 
Birch  Creek  district,  by  B.  L.  Johnson.  In  Bulletin  442,  1910,  pp.  246-250. 

Water  supply  of  the  Yukon-Tanana  region,  by  C.  E.  Ellsworth.  In  Bulletin  442, 
1910,  pp.  251-283. 

The  Koyukuk-Chandalar  gold  region,  by  A.  G.  Maddren.  In  Bulletin  442,  1910, 
pp.  284-315. 

Topographic  maps. 

Fortymile  quadrangle;  scale,  1:250,000;  by  E.  C.  Barnard.  For  sale  at  5 cents  a 
copy  or  $3  per  hundred. 

The  Fairbanks  quadrangle;  scale,  1:250,000;  by  T.  G.  Gerdine,  D.  C.  Witherspoon, 
and  R.  B.  Oliver.  For  sale  at  10  cents  a copy  or  $6  per  hundred. 

Rampart  quadrangle;  scale,  1:250,000;  by  D.  C.  Witherspoon  and  R.  B.  Oliver. 
For  sale  at  10  cents  a copy  or  $6  per  hundred. 

Fairbanks  special  map;  scale,  1:62,500;  by  T.  G.  Gerdine  and  R.  H.  Sargent.  For 
sale  at  10  cents  a copy  or  $6  per  hundred. 

Yukon-Tanana  region,  reconnaissance  map  of;  scale,  1 : 625,000;  by  T.  G.  Gerdine. 
Contained  in  Bulletin  251,  1905.  Not  published  separately. 

Fairbanks  and  Birch  Creek  districts,  reconnaissance  maps  of;  scale,  1 : 250,000;  by 
T.  G.  Gerdine.  Contained  in  Bulletin  251,  1905.  Not  issued  separately. 

Circle  quadrangle,  Yukon-Tanana  region;  scale,  1:250,000;  by  H.  C.  Witherspoon. 
Contained  in  Bulletin  295.  In  print  as  separate  publication. 

In  preparation. 

Geology  and  mineral  resources  of  Fairbanks  quadrangle,  by  L.  M.  Prindle. 

SEWARD  PENINSULA. 

A reconnaissance  of  the  Cape  Nome  and  adjacent  gold  fields  of  Seward  Peninsula, 
Alaska,  in  1900,  by  A.  H.  Brooks,  G.  B.  Richardson,  and  A.  J.  Collier.  In  a 
special  publication  entitled  “Reconnaissances  in  the  Cape  Nome  and  Norton 
Bay  regions,  Alaska,  in  1900,”  1901,  180  pp. 

A reconnaissance  in  the  Norton  Bay  region,  Alaska,  in  1900,  by  W.  C.  Mendenhall. 
In  a special  publication  entitled  “Reconnaissances  in  the  Cape  Nome  and 
Norton  Bay  regions,  Alaska,  in  1900,”  1901,  38  pp. 


54 


SURVEY  PUBLICATIONS  ON  ALASKA. 


A reconnaissance  of  the  northwestern  portion  of  Seward  Peninsula,  Alaska,  by  A.  J. 

Collier.  Professional  Paper  2,  1902,  70  pp. 

The  tin  deposits  of  the  York  region,  Alaska,  by  A.  J.  Collier.  Bulletin  229,  1904, 

Recent  developments  of  Alaskan  tin  deposits,  by  A.  J.  Collier.  In  Bulletin  259, 
1905,  pp.  120-127. 

The  Fairhaven  gold  placers  of  Seward  Peninsula,  by  F.  H.  Moffit.  Bulletin  247, 
1905,  85  pp. 

The  York  tin  region,  by  F.  L.  Hess.  In  Bulletin  284,  1906,  pp.  145-157. 

Gold  mining  on  Seward  Peninsula,  by  F.  H.  Moffit.  In  Bulletin  284, 1906,  pp.  132-141. 
The  Kougarok  region,  by  A.  H.  Brooks.  In  Bulletin  314,  1907,  pp.  164-181. 

*Water  supply  of  Nome  region,  Seward  Peninsula,  Alaska,  1906,  by  J.  C.  Hoyt  and 
F.  F.  Henshaw.  Water-Supply  Paper  196,  1907,  52  pp.  15  cents. 

Water  supply  of  the  Nome  region,  Seward  Peninsula,  1906,  by  J.  C.  Hoyt  and  F.  F. 

Henshaw.  In  Bulletin  314,  1907,  pp.  182-186. 

The  Nome  region,  by  F.  H.  Moffit.  In  Bulletin  314,  1907,  pp.  126-145. 

Gold  fields  of  the  Solomon  and  Niukluk  river  basins,  by  P.  S.  Smith.  In  Bulletin 
314,  1907,  pp.  146-156. 

Geology  and  mineral  resources  of  Iron  Creek,  by  P.  S.  Smith.  In  Bulletin  314, 

1907,  pp.  157-163. 

The  gold  placers  of  parts  of  Seward  Peninsula,  Alaska,  including  the  Nome,  Council, 
Kougarok,  Port  Clarence,  and  Goodhope  precincts,  by  A.  J.  Collier,  F.  L.  Hess, 
P.  S.  Smith,  and  A.  H.  Brooks.  Bulletin  328,  1908,  343  pp. 

*Investigation  of  the  mineral  deposits  of  Seward  Peninsula,  by  P.  S.  Smith.  In 
Bulletin  345,  1908,  pp.  206-250.  45  cents. 

*The  Seward  Peninsula  tin  deposits,  by  Adolph  Knopf.  In  Bulletin  345,  1908, 
pp.  251-267.  45  cents. 

*Mineral  deposits  of  the  Lost  River  and  Brooks  Mountain  regions,  Seward  Peninsula, 
by  Adolph  Knopf.  In  Bulletin  345,  1908,  pp.  268-271.  45  cents. 

*Water  supply  of  the  Nome  and  Kougarok  regions,  Seward  Peninsula,  in  1906-7,  by 
F.  F.  Henshaw.  In  Bulletin  345,  1908,  pp.  272-285.  45  cents. 

Water-supply  investigations  in  Alaska,  1906  and  1907,  by  F.  F.  Henshaw  and  C.  C. 

Covert.  Water-Supply  Paper  218,  1908,  156  pp. 

Geology  of  the  Seward  Peninsula  tin  deposits,  by  Adolph  Knopf.  Bulletin  358, 

1908,  72  pp. 

Recent  developments  in  southern  Seward  Peninsula,  by  P.  S.  Smith.  In  Bulletin 
379,  1909,  pp.  267-301. 

The  Iron  Creek  region,  by  P.  S.  Smith.  In  Bulletin  379,  1909,  pp.  302-354. 
Mining  in  the  Fairhaven  precinct,  by  F.  F.  Henshaw.  In  Bulletin  379, 1909,  pp.  355- 
369. 

Water-supply  investigations  in  Seward  Peninsula  in  1908,  by  F.  F.  Henshaw.  In 
Bulletin  379,  1909,  pp.  370-401. 

Geology  and  mineral  resources  of  the  Solomon  and  Casadepaga  quadrangles,  Seward 
Peninsula,  by  P.  S.  Smith.  Bulletin  433,  1910,  227  pp. 

Mineral  resources  of  the  Nulato-Council  region,  by  P.  S.  Smith  and  H.  M.  Eakin. 
In  Bulletin  442,  1910,  pp.  316-352. 

Mining  in  Seward  Peninsula,  by  F.  F.  Henshaw.  In  Bulletin  442,  1910,  pp.  353- 
371. 

Water-supply  investigations  in  Seward  Peninsula  in  1909,  by  F.  F.  Henshaw.  In 
Bulletin  442,  1910,  pp.  372-418. 

Topographic  maps. 

The  following  maps  are  for  sale  at  5 cents  a copy  or  $3  per  hundred: 

Casadepaga  quadrangle,  Seward  Peninsula;  scale,  1:62,500;  by  T.  G.  Gerdine. 
Grand  Central  special,  Seward  Peninsula;  scale,  1:62,500;  by  T.  G.  Gerdine. 

Nome  special,  Seward  Peninsula;  scale,  1:  62,500;  by  T.  G.  Gerdine. 

Solomon  quadrangle,  Seward  Peninsula;  scale,  1:  62,500;  by  T.  G.  Gerdine. 

The  following  maps  are  for  sale  at  25  cents  a copy  or  $15  per  hundred: 

Seward  Peninsula,  northeastern  portion  of,  topographic  reconnaissance  of;  scale, 
1:250,000;  by  T.G.  Gerdine. 

Seward  Peninsula,  northwestern  portion  of,  topographic  reconnaissance  of;  scale, 
1:  250,000;  by  T.  G.  Gerdine. 

Seward  Peninsula,  southern  portion  of,  topographic  reconnaissance  of;  scale,  1:250,- 
000;  by  T.  G.  Gerdine. 


SURVEY  PUBLICATIONS  ON  ALASKA. 


55 


hi  press. 

A geologic  reconnaissance  in  soulheastern  Seward  Peninsula  and  the  Norton  Bay- 
Nulato  region,  by  P.  S.  Smith  and  II.  M.  Eakin.  Bulletin  449. 

hi  preparatiori. 

Geology  of  the  area  represented  on  the  Nome  and  Grand  Central  special  maps,  by 
F.  H.  Motht,  F.  L.  Hess,  and  P.  S.  Smith. 

The  water  resources  of  the  Seward  Peninsida,  by  F.  F\  Ilenshaw. 

NORTHERN  ALASKA. 

A reconnaissance  from  Fort  Hamlin  to  Kotzebue  Sound,  Alaska,  by  way  of  Dali, 
Kanuti,  Allen,  and  Kowak  rivers,  1)V  W.  C.  Mendenhall.  Professional  Paper  10, 
1902,  G8  pp.  _ “ _ ■ 

*A  reconnaissance  in  northern  Alaska  across  the  Rocky  Mountains,  along  the  Koyukuk, 
John,  Anaktuviik,  and  Colville  rivers,  and  the  Arctic  coast  to  Cape  Lisburne, 
in  1901,  by  F.  C.  Schrader  and  W.  J.  Peters.  Professional  Paper  20,  1904,  139  pp. 

Coal  fields  of  the  Cape  Lisburne  region,  by  A.  J.  Collier.  In  Bulletin  259,  1905, 
pp.  172-185. 

Geology  and  coal  resources  of  Cape  Idsburne  region,  Alaska,  by  A.  J.  Collier.  Bulle- 
tin 278,  1906,  54  pp. 

Topographic  maps. 

Fort  Yukon  to  Kotzebue  Sound,  reconnaissance  map  of;  scale,  1: 1,200,000;  by  D.  L. 
Reaburn.  Contained  in  Professional  Paper  10.  Not  published  separately. 
*Koyukuk  River  to  mouth  of  Colville  River,  including  John  River;  scale,  1: 1,200,000; 
by  W.  J.  Peters.  Contained  in  Professional  Paper  20.  Not  published  separately. 


INDEX, 


A.  Page. 

Access  to  the  region,  means  of 9 

B. 

Basic  volcanic  rocks,  age  of 21 

description  of 19 

dikes  in 21 

metamorphism  of 20-21 

petrography  of 19-20 

Bear  mine,  description  of 39-40 

metamorphism  in 33 

Becker,  G.  F.,  work  of 5 

Berners  Bay,  description  of 9-10 

Berners  Bay  Mining  & Milling  Co.,  legal 

troubles  of 8 

Berners  formation,  age,  and  correlation  of. . . 17 

description  of 12-13, 14-15 

fossils  in 17 

dikes  in 18-19 

petrography  of 16-17 

Brooks,  A.  H.,  preface  by 5-6 

C. 

Calcite,  occurrence  of 30 

, Chalcopyrite,  occurrence  of 29 

1 Chlorite,  occurrence  of 31 

I Climate,  character  of 10 

' data  on 11 

j Comet,  town  of 8 

' Comet  mine,  description  of 42-43 

j production  of 8, 43 

j Copper,  occurrence  of 29 

D. 

Dikes,  description  of 13,18-19,21,24 

Dolomite,  occurrence  of 30 

E. 

Epidote,  occurrence  of 31 

Eureka  mine,  description  of 42 

F. 

Feldspar,  occurrence  of 30 

Felsites,  intrusive  occurrence  of 21 

Field  work,  progress  of 7-8 

Fissure  veins.  See  Veins. 

Fossils,  occurrence  and  character  of 17 

Fremming  property,  description  of 47 

G. 

Galena,  occurrence  of 29 

Geography,  outline  of 9-12 

Geology,  description  of 6, 12-26 

Glaciation,  description  of 12 

influence  of,  on  ore  deposits 36 

Gold,  occurrence  of 29 

Graywackes,  occurrence  of 16 


Page. 

Greek  Boy  property,  description  o 47-48 

Greenstones,  age  of 6 

II. 

History,  outline  of 8 

Hornblende,  occurrence  of 31 

Hornblendite,  description  of 25-26 

Horrible  mine,  description  of 39 

I. 

Independence  Creek,  rocks  on 15, 18, 19 

Independence  Gulch,  rocks  in 20 

Indiana  property,  description  of 44 

International  Trust  Co.,  purchase  of  property 

by 8 

Intrusive  rocks,  description  of 13,21,24 

Ivanhoe  mine,  description  of 38-39 

J. 

Johnson  Creek,  description  of 10 

rocks  on 18,24 

Johnson  mine,  description  of 43-44 

Jualin  Cove,  rocks  at 16 

Jualin  diorite,  age  of 25 

description  of 13-14, 24 

intrusion  of 20, 24 

ores  in 14 

petrography  of 24-25 

J ualin  mine,  description  of 44 

metamorphism  at 33, 46-47 

ores  of 37,45-47 

Juneau,  climate  of 11 

Juneau  region,  mines  of 7 

K. 

Kensington  mine,  description  of 40-42 

section  in,  figure  showing 41 

stockwork  in,  metamorphism  at 33,41 

Knowlton,  F.  H.,  fossils  determined  by 17 

L. 

Lamprophyric  dikes 18, 41-42 

Lavas,  description  of 13 

See  also  Basic  volcanic  rocks. 

Litigation,  troubles  with 5-6, 8 

Location  of  region 7,9 

Lynn  Canal,  description  of 10 

M. 

Magma,  vein-forming  waters  from 35-36 

Metabasalts.  {See  Basic  volcanic  rocks.) 
Metamorphism,  occurrence  and  character 

of 14,20,-35-36 

Mines,  description  of 38-48 

Mining  development,  progress  of 6 

Moraines,  location  of 12 

57 


i 


58 


INDEX. 


O.  Page. 

Ophir  group,  description  of 39 

Ore  deposits,  conclusions  on 36-38 

continuity  of,  in  depth 37-38 

minerals  of 29-31 

occurrence  and  character  of 14, 26-28 

origin  of 35-36 

See  also  Mines. 

Ores,  value  of 31 

P. 

Production,  records  of 8 

Pyrite,  occurrence  of 30 

Q. 

Quartz,  occurrence  of 30 

Quartz  diorite  gneiss,  age  of 23 

description  of 13,14,22 

metainorphism  of 23-24 

mineralogical,  analy.sis  of 23 

petrography  of 22-23 

Quartz  porphyry  schist,  occurrence  of 18 

S. 

Sericite,  occurrence  of 30 

Seward,  city  of 8 

Sherman  Creek,  de.scription  of 10 


Page. 

Sherman  rocks  on 24 

Skagway,  climate  of 11 

Solutions,  hot  ascending,  deposition  by 34 

Spencer,  A.  C.,  work  of 7,24,35-36 

Sphalerite,  occurrence  of 29 

Stockworks,  description  of ’ 28 

Stringer  lodes,  description  of 28 

Surveys,  progress  of 5-6 

T. 

Topography,  description  of 6,9-10 

view  showing 9 

Transportation,  means  of 9 

V. 

Vegetation,  character  of 11-12 

Veins,  description  of 26-28 

dip  of,  figure  showing 27 

strike  of,  figure  showing 27 

formation  of 31-34 

Volcanic  rocks.  (See  Basic  volcanic  rocks.) 

W. 

Waters,  vein-forming,  origin  of 35-36 

Wright,  C.  W.,  work  of 17,24 


O 


T()1>0(VHAPHI(’  MAP  OK  BKRXKHS  RA"i’ HKOIOX.  ALASKA 


1910 


U S GtOLOOICAL  SURVEY 
OEORGf  OTIS  SMITH  DIRECTOR 


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PLATE 


GEOLOGIC  \L\P  OF  BEHXERS  BAY  HKGION,  ALASIGV 

Srjile  Aa^oD 


Silt  mid  ^ravol  ) g. 


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1910 


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